{"id":1415,"date":"2024-06-02T23:01:09","date_gmt":"2024-06-02T23:01:09","guid":{"rendered":""},"modified":"2024-06-05T06:12:46","modified_gmt":"2024-06-04T22:12:46","slug":"typescript-%e4%b9%8b%e5%b8%b8%e8%a7%81%e7%b1%bb%e5%9e%8b%ef%bc%88%e4%b8%8b%ef%bc%89","status":"publish","type":"post","link":"https:\/\/www.lccc.top\/?p=1415","title":{"rendered":"TypeScript \u4e4b\u5e38\u89c1\u7c7b\u578b\uff08\u4e0b\uff09"},"content":{"rendered":"<td class=\"d-block comment-body markdown-body  js-comment-body\">\n<blockquote>\n<p dir=\"auto\">TypeScript \u7684\u5b98\u65b9\u6587\u6863\u65e9\u5df2\u66f4\u65b0\uff0c\u4f46\u6211\u80fd\u627e\u5230\u7684\u4e2d\u6587\u6587\u6863\u90fd\u8fd8\u505c\u7559\u5728\u6bd4\u8f83\u8001\u7684\u7248\u672c\u3002\u6240\u4ee5\u5bf9\u5176\u4e2d\u65b0\u589e\u4ee5\u53ca\u4fee\u8ba2\u8f83\u591a\u7684\u4e00\u4e9b\u7ae0\u8282\u8fdb\u884c\u4e86\u7ffb\u8bd1\u6574\u7406\u3002<\/p>\n<\/blockquote>\n<blockquote>\n<p dir=\"auto\">\u672c\u7bc7\u7ffb\u8bd1\u6574\u7406\u81ea TypeScript Handbook \u4e2d \u300c<a href=\"https:\/\/www.typescriptlang.org\/docs\/handbook\/2\/everyday-types.html\" rel=\"nofollow\">Everyday Types<\/a>\u300d \u7ae0\u8282\u3002<\/p>\n<\/blockquote>\n<blockquote>\n<p dir=\"auto\">\u672c\u6587\u5e76\u4e0d\u4e25\u683c\u6309\u7167\u539f\u6587\u7ffb\u8bd1\uff0c\u5bf9\u90e8\u5206\u5185\u5bb9\u4e5f\u505a\u4e86\u89e3\u91ca\u8865\u5145\u3002<\/p>\n<\/blockquote>\n<h2 dir=\"auto\">\u7c7b\u578b\u522b\u540d\uff08Type Aliases\uff09<\/h2>\n<p dir=\"auto\">\u6211\u4eec\u5df2\u7ecf\u5b66\u4f1a\u5728\u7c7b\u578b\u6ce8\u89e3\u91cc\u76f4\u63a5\u4f7f\u7528\u5bf9\u8c61\u7c7b\u578b\u548c\u8054\u5408\u7c7b\u578b\uff0c\u8fd9\u5f88\u65b9\u4fbf\uff0c\u4f46\u6709\u7684\u65f6\u5019\uff0c\u4e00\u4e2a\u7c7b\u578b\u4f1a\u88ab\u4f7f\u7528\u591a\u6b21\uff0c\u6b64\u65f6\u6211\u4eec\u66f4\u5e0c\u671b\u901a\u8fc7\u4e00\u4e2a\u5355\u72ec\u7684\u540d\u5b57\u6765\u5f15\u7528\u5b83\u3002<\/p>\n<p dir=\"auto\">\u8fd9\u5c31\u662f\u7c7b\u578b\u522b\u540d\uff08type alias\uff09\u3002\u6240\u8c13\u7c7b\u578b\u522b\u540d\uff0c\u987e\u540d\u601d\u4e49\uff0c\u4e00\u4e2a\u53ef\u4ee5\u6307\u4ee3\u4efb\u610f\u7c7b\u578b\u7684\u540d\u5b57\u3002\u7c7b\u578b\u522b\u540d\u7684\u8bed\u6cd5\u662f\uff1a<\/p>\n<div class=\"highlight highlight-source-ts notranslate position-relative overflow-auto\" dir=\"auto\" data-snippet-clipboard-copy-content=\"type Point = {\n  x: number;\n  y: number;\n};\n \n\/\/ Exactly the same as the earlier example\nfunction printCoord(pt: Point) {\n  console.log(&quot;The coordinate's x value is &quot; + pt.x);\n  console.log(&quot;The coordinate's y value is &quot; + pt.y);\n}\n \nprintCoord({ x: 100, y: 100 });\"><\/p>\n<pre class=\"notranslate\"><span class=\"pl-k\">type<\/span> <span class=\"pl-smi\">Point<\/span> <span class=\"pl-c1\">=<\/span> <span class=\"pl-kos\">{<\/span>\n  <span class=\"pl-c1\">x<\/span>: <span class=\"pl-smi\">number<\/span><span class=\"pl-kos\">;<\/span>\n  <span class=\"pl-c1\">y<\/span>: <span class=\"pl-smi\">number<\/span><span class=\"pl-kos\">;<\/span>\n<span class=\"pl-kos\">}<\/span><span class=\"pl-kos\">;<\/span>\n \n<span class=\"pl-c\">\/\/ Exactly the same as the earlier example<\/span>\n<span class=\"pl-k\">function<\/span> <span class=\"pl-en\">printCoord<\/span><span class=\"pl-kos\">(<\/span><span class=\"pl-s1\">pt<\/span>: <span class=\"pl-smi\">Point<\/span><span class=\"pl-kos\">)<\/span> <span class=\"pl-kos\">{<\/span>\n  <span class=\"pl-smi\">console<\/span><span class=\"pl-kos\">.<\/span><span class=\"pl-en\">log<\/span><span class=\"pl-kos\">(<\/span><span class=\"pl-s\">\"The coordinate's x value is \"<\/span> <span class=\"pl-c1\">+<\/span> <span class=\"pl-s1\">pt<\/span><span class=\"pl-kos\">.<\/span><span class=\"pl-c1\">x<\/span><span class=\"pl-kos\">)<\/span><span class=\"pl-kos\">;<\/span>\n  <span class=\"pl-smi\">console<\/span><span class=\"pl-kos\">.<\/span><span class=\"pl-en\">log<\/span><span class=\"pl-kos\">(<\/span><span class=\"pl-s\">\"The coordinate's y value is \"<\/span> <span class=\"pl-c1\">+<\/span> <span class=\"pl-s1\">pt<\/span><span class=\"pl-kos\">.<\/span><span class=\"pl-c1\">y<\/span><span class=\"pl-kos\">)<\/span><span class=\"pl-kos\">;<\/span>\n<span class=\"pl-kos\">}<\/span>\n \n<span class=\"pl-en\">printCoord<\/span><span class=\"pl-kos\">(<\/span><span class=\"pl-kos\">{<\/span> <span class=\"pl-c1\">x<\/span>: <span class=\"pl-c1\">100<\/span><span class=\"pl-kos\">,<\/span> <span class=\"pl-c1\">y<\/span>: <span class=\"pl-c1\">100<\/span> <span class=\"pl-kos\">}<\/span><span class=\"pl-kos\">)<\/span><span class=\"pl-kos\">;<\/span><\/pre>\n<\/div>\n<p dir=\"auto\">\u4f60\u53ef\u4ee5\u4f7f\u7528\u7c7b\u578b\u522b\u540d\u7ed9\u4efb\u610f\u7c7b\u578b\u4e00\u4e2a\u540d\u5b57\uff0c\u4e3e\u4e2a\u4f8b\u5b50\uff0c\u547d\u540d\u4e00\u4e2a\u8054\u5408\u7c7b\u578b\uff1a<\/p>\n<div class=\"highlight highlight-source-ts notranslate position-relative overflow-auto\" dir=\"auto\" data-snippet-clipboard-copy-content=\"type ID = number | string;\">\n<pre class=\"notranslate\"><span class=\"pl-k\">type<\/span> <span class=\"pl-smi\">ID<\/span> <span class=\"pl-c1\">=<\/span> <span class=\"pl-smi\">number<\/span> <span class=\"pl-c1\">|<\/span> <span class=\"pl-smi\">string<\/span><span class=\"pl-kos\">;<\/span><\/pre>\n<\/div>\n<p dir=\"auto\">\u6ce8\u610f\u522b\u540d\u662f\u552f\u4e00\u7684\u522b\u540d\uff0c\u4f60\u4e0d\u80fd\u4f7f\u7528\u7c7b\u578b\u522b\u540d\u521b\u5efa\u540c\u4e00\u4e2a\u7c7b\u578b\u7684\u4e0d\u540c\u7248\u672c\u3002\u5f53\u4f60\u4f7f\u7528\u7c7b\u578b\u522b\u540d\u7684\u65f6\u5019\uff0c\u5b83\u5c31\u8ddf\u4f60\u7f16\u5199\u7684\u7c7b\u578b\u662f\u4e00\u6837\u7684\u3002\u6362\u53e5\u8bdd\u8bf4\uff0c\u4ee3\u7801\u770b\u8d77\u6765\u53ef\u80fd\u4e0d\u5408\u6cd5\uff0c\u4f46\u5bf9 TypeScript \u4f9d\u7136\u662f\u5408\u6cd5\u7684\uff0c\u56e0\u4e3a\u4e24\u4e2a\u7c7b\u578b\u90fd\u662f\u540c\u4e00\u4e2a\u7c7b\u578b\u7684\u522b\u540d:<\/p>\n<div class=\"highlight highlight-source-ts notranslate position-relative overflow-auto\" dir=\"auto\" data-snippet-clipboard-copy-content='type UserInputSanitizedString = string;\n \nfunction sanitizeInput(str: string): UserInputSanitizedString {\n  return sanitize(str);\n}\n \n\/\/ Create a sanitized input\nlet userInput = sanitizeInput(getInput());\n \n\/\/ Can still be re-assigned with a string though\nuserInput = \"new input\";'><\/p>\n<pre class=\"notranslate\"><span class=\"pl-k\">type<\/span> <span class=\"pl-smi\">UserInputSanitizedString<\/span> <span class=\"pl-c1\">=<\/span> <span class=\"pl-smi\">string<\/span><span class=\"pl-kos\">;<\/span>\n \n<span class=\"pl-k\">function<\/span> <span class=\"pl-en\">sanitizeInput<\/span><span class=\"pl-kos\">(<\/span><span class=\"pl-s1\">str<\/span>: <span class=\"pl-smi\">string<\/span><span class=\"pl-kos\">)<\/span>: <span class=\"pl-smi\">UserInputSanitizedString<\/span> <span class=\"pl-kos\">{<\/span>\n  <span class=\"pl-k\">return<\/span> <span class=\"pl-en\">sanitize<\/span><span class=\"pl-kos\">(<\/span><span class=\"pl-s1\">str<\/span><span class=\"pl-kos\">)<\/span><span class=\"pl-kos\">;<\/span>\n<span class=\"pl-kos\">}<\/span>\n \n<span class=\"pl-c\">\/\/ Create a sanitized input<\/span>\n<span class=\"pl-k\">let<\/span> <span class=\"pl-s1\">userInput<\/span> <span class=\"pl-c1\">=<\/span> <span class=\"pl-en\">sanitizeInput<\/span><span class=\"pl-kos\">(<\/span><span class=\"pl-en\">getInput<\/span><span class=\"pl-kos\">(<\/span><span class=\"pl-kos\">)<\/span><span class=\"pl-kos\">)<\/span><span class=\"pl-kos\">;<\/span>\n \n<span class=\"pl-c\">\/\/ Can still be re-assigned with a string though<\/span>\n<span class=\"pl-s1\">userInput<\/span> <span class=\"pl-c1\">=<\/span> <span class=\"pl-s\">\"new input\"<\/span><span class=\"pl-kos\">;<\/span><\/pre>\n<\/div>\n<h2 dir=\"auto\">\u63a5\u53e3\uff08Interfaces\uff09<\/h2>\n<p dir=\"auto\">\u63a5\u53e3\u58f0\u660e\uff08interface declaration\uff09\u662f\u547d\u540d\u5bf9\u8c61\u7c7b\u578b\u7684\u53e6\u4e00\u79cd\u65b9\u5f0f\uff1a<\/p>\n<div class=\"highlight highlight-source-ts notranslate position-relative overflow-auto\" dir=\"auto\" data-snippet-clipboard-copy-content=\"interface Point {\n  x: number;\n  y: number;\n}\n \nfunction printCoord(pt: Point) {\n  console.log(&quot;The coordinate's x value is &quot; + pt.x);\n  console.log(&quot;The coordinate's y value is &quot; + pt.y);\n}\n \nprintCoord({ x: 100, y: 100 });\"><\/p>\n<pre class=\"notranslate\"><span class=\"pl-k\">interface<\/span> <span class=\"pl-smi\">Point<\/span> <span class=\"pl-kos\">{<\/span>\n  <span class=\"pl-c1\">x<\/span>: <span class=\"pl-smi\">number<\/span><span class=\"pl-kos\">;<\/span>\n  <span class=\"pl-c1\">y<\/span>: <span class=\"pl-smi\">number<\/span><span class=\"pl-kos\">;<\/span>\n<span class=\"pl-kos\">}<\/span>\n \n<span class=\"pl-k\">function<\/span> <span class=\"pl-en\">printCoord<\/span><span class=\"pl-kos\">(<\/span><span class=\"pl-s1\">pt<\/span>: <span class=\"pl-smi\">Point<\/span><span class=\"pl-kos\">)<\/span> <span class=\"pl-kos\">{<\/span>\n  <span class=\"pl-smi\">console<\/span><span class=\"pl-kos\">.<\/span><span class=\"pl-en\">log<\/span><span class=\"pl-kos\">(<\/span><span class=\"pl-s\">\"The coordinate's x value is \"<\/span> <span class=\"pl-c1\">+<\/span> <span class=\"pl-s1\">pt<\/span><span class=\"pl-kos\">.<\/span><span class=\"pl-c1\">x<\/span><span class=\"pl-kos\">)<\/span><span class=\"pl-kos\">;<\/span>\n  <span class=\"pl-smi\">console<\/span><span class=\"pl-kos\">.<\/span><span class=\"pl-en\">log<\/span><span class=\"pl-kos\">(<\/span><span class=\"pl-s\">\"The coordinate's y value is \"<\/span> <span class=\"pl-c1\">+<\/span> <span class=\"pl-s1\">pt<\/span><span class=\"pl-kos\">.<\/span><span class=\"pl-c1\">y<\/span><span class=\"pl-kos\">)<\/span><span class=\"pl-kos\">;<\/span>\n<span class=\"pl-kos\">}<\/span>\n \n<span class=\"pl-en\">printCoord<\/span><span class=\"pl-kos\">(<\/span><span class=\"pl-kos\">{<\/span> <span class=\"pl-c1\">x<\/span>: <span class=\"pl-c1\">100<\/span><span class=\"pl-kos\">,<\/span> <span class=\"pl-c1\">y<\/span>: <span class=\"pl-c1\">100<\/span> <span class=\"pl-kos\">}<\/span><span class=\"pl-kos\">)<\/span><span class=\"pl-kos\">;<\/span><\/pre>\n<\/div>\n<p dir=\"auto\">\u5c31\u50cf\u6211\u4eec\u5728\u4e0a\u8282\u4f7f\u7528\u7684\u7c7b\u578b\u522b\u540d\uff0c\u8fd9\u4e2a\u4f8b\u5b50\u4e5f\u540c\u6837\u53ef\u4ee5\u8fd0\u884c\uff0c\u5c31\u8ddf\u6211\u4eec\u4f7f\u7528\u4e86\u4e00\u4e2a\u533f\u540d\u5bf9\u8c61\u7c7b\u578b\u4e00\u6837\u3002TypeScript \u53ea\u5173\u5fc3\u4f20\u9012\u7ed9 <code class=\"notranslate\">printCoord<\/code> \u7684\u503c\u7684\u7ed3\u6784\uff08structure\uff09\u2014\u2014\u5173\u5fc3\u503c\u662f\u5426\u6709\u671f\u671b\u7684\u5c5e\u6027\u3002\u6b63\u662f\u8fd9\u79cd\u53ea\u5173\u5fc3\u7c7b\u578b\u7684\u7ed3\u6784\u548c\u80fd\u529b\u7684\u7279\u6027\uff0c\u6211\u4eec\u624d\u8ba4\u4e3a TypeScript \u662f\u4e00\u4e2a\u7ed3\u6784\u5316\uff08structurally\uff09\u7684\u7c7b\u578b\u7cfb\u7edf\u3002<\/p>\n<h3 dir=\"auto\">\u7c7b\u578b\u522b\u540d\u548c\u63a5\u53e3\u7684\u4e0d\u540c<\/h3>\n<p dir=\"auto\">\u7c7b\u578b\u522b\u540d\u548c\u63a5\u53e3\u975e\u5e38\u76f8\u4f3c\uff0c\u5927\u90e8\u5206\u65f6\u5019\uff0c\u4f60\u53ef\u4ee5\u4efb\u610f\u9009\u62e9\u4f7f\u7528\u3002\u63a5\u53e3\u7684\u51e0\u4e4e\u6240\u6709\u7279\u6027\u90fd\u53ef\u4ee5\u5728 <code class=\"notranslate\">type<\/code> \u4e2d\u4f7f\u7528\uff0c\u4e24\u8005\u6700\u5173\u952e\u7684\u5dee\u522b\u5728\u4e8e\u7c7b\u578b\u522b\u540d\u672c\u8eab\u65e0\u6cd5\u6dfb\u52a0\u65b0\u7684\u5c5e\u6027\uff0c\u800c\u63a5\u53e3\u662f\u53ef\u4ee5\u6269\u5c55\u7684\u3002<\/p>\n<div class=\"highlight highlight-source-ts notranslate position-relative overflow-auto\" dir=\"auto\" data-snippet-clipboard-copy-content=\"\/\/ Interface\n\/\/ \u901a\u8fc7\u7ee7\u627f\u6269\u5c55\u7c7b\u578b\ninterface Animal {\n  name: string\n}\n\ninterface Bear extends Animal {\n  honey: boolean\n}\n\nconst bear = getBear() \nbear.name\nbear.honey\n        \n\/\/ Type\n\/\/ \u901a\u8fc7\u4ea4\u96c6\u6269\u5c55\u7c7b\u578b\ntype Animal = {\n  name: string\n}\n\ntype Bear = Animal &amp; { \n  honey: boolean \n}\n\nconst bear = getBear();\nbear.name;\nbear.honey;\"><\/p>\n<pre class=\"notranslate\"><span class=\"pl-c\">\/\/ Interface<\/span>\n<span class=\"pl-c\">\/\/ \u901a\u8fc7\u7ee7\u627f\u6269\u5c55\u7c7b\u578b<\/span>\n<span class=\"pl-k\">interface<\/span> <span class=\"pl-smi\">Animal<\/span> <span class=\"pl-kos\">{<\/span>\n  <span class=\"pl-c1\">name<\/span>: <span class=\"pl-smi\">string<\/span>\n<span class=\"pl-kos\">}<\/span>\n\n<span class=\"pl-k\">interface<\/span> <span class=\"pl-smi\">Bear<\/span> <span class=\"pl-k\">extends<\/span> <span class=\"pl-smi\">Animal<\/span> <span class=\"pl-kos\">{<\/span>\n  <span class=\"pl-c1\">honey<\/span>: <span class=\"pl-smi\">boolean<\/span>\n<span class=\"pl-kos\">}<\/span>\n\n<span class=\"pl-k\">const<\/span> <span class=\"pl-s1\">bear<\/span> <span class=\"pl-c1\">=<\/span> <span class=\"pl-en\">getBear<\/span><span class=\"pl-kos\">(<\/span><span class=\"pl-kos\">)<\/span> \n<span class=\"pl-s1\">bear<\/span><span class=\"pl-kos\">.<\/span><span class=\"pl-c1\">name<\/span>\n<span class=\"pl-s1\">bear<\/span><span class=\"pl-kos\">.<\/span><span class=\"pl-c1\">honey<\/span>\n        \n<span class=\"pl-c\">\/\/ Type<\/span>\n<span class=\"pl-c\">\/\/ \u901a\u8fc7\u4ea4\u96c6\u6269\u5c55\u7c7b\u578b<\/span>\n<span class=\"pl-k\">type<\/span> <span class=\"pl-smi\">Animal<\/span> <span class=\"pl-c1\">=<\/span> <span class=\"pl-kos\">{<\/span>\n  <span class=\"pl-c1\">name<\/span>: <span class=\"pl-smi\">string<\/span>\n<span class=\"pl-kos\">}<\/span>\n\n<span class=\"pl-k\">type<\/span> <span class=\"pl-smi\">Bear<\/span> <span class=\"pl-c1\">=<\/span> <span class=\"pl-smi\">Animal<\/span> <span class=\"pl-c1\">&amp;<\/span> <span class=\"pl-kos\">{<\/span> \n  <span class=\"pl-c1\">honey<\/span>: <span class=\"pl-smi\">boolean<\/span> \n<span class=\"pl-kos\">}<\/span>\n\n<span class=\"pl-k\">const<\/span> <span class=\"pl-s1\">bear<\/span> <span class=\"pl-c1\">=<\/span> <span class=\"pl-en\">getBear<\/span><span class=\"pl-kos\">(<\/span><span class=\"pl-kos\">)<\/span><span class=\"pl-kos\">;<\/span>\n<span class=\"pl-s1\">bear<\/span><span class=\"pl-kos\">.<\/span><span class=\"pl-c1\">name<\/span><span class=\"pl-kos\">;<\/span>\n<span class=\"pl-s1\">bear<\/span><span class=\"pl-kos\">.<\/span><span class=\"pl-c1\">honey<\/span><span class=\"pl-kos\">;<\/span><\/pre>\n<\/div>\n<div class=\"highlight highlight-source-ts notranslate position-relative overflow-auto\" dir=\"auto\" data-snippet-clipboard-copy-content=\"\/\/ Interface\n\/\/ \u5bf9\u4e00\u4e2a\u5df2\u7ecf\u5b58\u5728\u7684\u63a5\u53e3\u6dfb\u52a0\u65b0\u7684\u5b57\u6bb5\ninterface Window {\n  title: string\n}\n\ninterface Window {\n  ts: TypeScriptAPI\n}\n\nconst src = 'const a = &quot;Hello World&quot;';\nwindow.ts.transpileModule(src, {});\n        \n\/\/ Type\n\/\/ \u521b\u5efa\u540e\u4e0d\u80fd\u88ab\u6539\u53d8\ntype Window = {\n  title: string\n}\n\ntype Window = {\n  ts: TypeScriptAPI\n}\n\n\/\/ Error: Duplicate identifier 'Window'.\"><\/p>\n<pre class=\"notranslate\"><span class=\"pl-c\">\/\/ Interface<\/span>\n<span class=\"pl-c\">\/\/ \u5bf9\u4e00\u4e2a\u5df2\u7ecf\u5b58\u5728\u7684\u63a5\u53e3\u6dfb\u52a0\u65b0\u7684\u5b57\u6bb5<\/span>\n<span class=\"pl-k\">interface<\/span> <span class=\"pl-smi\">Window<\/span> <span class=\"pl-kos\">{<\/span>\n  <span class=\"pl-c1\">title<\/span>: <span class=\"pl-smi\">string<\/span>\n<span class=\"pl-kos\">}<\/span>\n\n<span class=\"pl-k\">interface<\/span> <span class=\"pl-smi\">Window<\/span> <span class=\"pl-kos\">{<\/span>\n  <span class=\"pl-c1\">ts<\/span>: <span class=\"pl-smi\">TypeScriptAPI<\/span>\n<span class=\"pl-kos\">}<\/span>\n\n<span class=\"pl-k\">const<\/span> <span class=\"pl-s1\">src<\/span> <span class=\"pl-c1\">=<\/span> <span class=\"pl-s\">'const a = \"Hello World\"'<\/span><span class=\"pl-kos\">;<\/span>\n<span class=\"pl-smi\">window<\/span><span class=\"pl-kos\">.<\/span><span class=\"pl-c1\">ts<\/span><span class=\"pl-kos\">.<\/span><span class=\"pl-en\">transpileModule<\/span><span class=\"pl-kos\">(<\/span><span class=\"pl-s1\">src<\/span><span class=\"pl-kos\">,<\/span> <span class=\"pl-kos\">{<\/span><span class=\"pl-kos\">}<\/span><span class=\"pl-kos\">)<\/span><span class=\"pl-kos\">;<\/span>\n        \n<span class=\"pl-c\">\/\/ Type<\/span>\n<span class=\"pl-c\">\/\/ \u521b\u5efa\u540e\u4e0d\u80fd\u88ab\u6539\u53d8<\/span>\n<span class=\"pl-k\">type<\/span> <span class=\"pl-smi\">Window<\/span> <span class=\"pl-c1\">=<\/span> <span class=\"pl-kos\">{<\/span>\n  <span class=\"pl-c1\">title<\/span>: <span class=\"pl-smi\">string<\/span>\n<span class=\"pl-kos\">}<\/span>\n\n<span class=\"pl-k\">type<\/span> <span class=\"pl-smi\">Window<\/span> <span class=\"pl-c1\">=<\/span> <span class=\"pl-kos\">{<\/span>\n  <span class=\"pl-c1\">ts<\/span>: <span class=\"pl-smi\">TypeScriptAPI<\/span>\n<span class=\"pl-kos\">}<\/span>\n\n<span class=\"pl-c\">\/\/ Error: Duplicate identifier 'Window'.<\/span><\/pre>\n<\/div>\n<p dir=\"auto\">\u5728\u540e\u7eed\u7684\u7ae0\u8282\u91cc\uff0c\u4f60\u8fd8\u4f1a\u4e86\u89e3\u7684\u66f4\u591a\u3002\u6240\u4ee5\u4e0b\u9762\u8fd9\u4e9b\u5185\u5bb9\u4e0d\u80fd\u7acb\u523b\u7406\u89e3\u4e5f\u6ca1\u6709\u5173\u7cfb\uff1a<\/p>\n<ul dir=\"auto\">\n<li>\u5728 TypeScript 4.2 \u4ee5\u524d\uff0c<a href=\"https:\/\/www.typescriptlang.org\/play?#code\/PTAEGEHsFsAcEsA2BTATqNrLusgzngIYDm+oA7koqIYuYQJ56gCueyoAUCKAC4AWHAHaFcoSADMaQ0PCG80EwgGNkALk6c5C1EtWgAsqOi1QAb06groEbjWg8vVHOKcAvpokshy3vEgyyMr8kEbQJogAFND2YREAlOaW1soBeJAoAHSIkMTRmbbI8e6aPMiZxJmgACqCGKhY6ABGyDnkFFQ0dIzMbBwCwqIccabcYLyQoKjIEmh8kwN8DLAc5PzwwbLMyAAeK77IACYaQSEjUWZWhfYAjABMAMwALA+gbsVjoADqgjKESytQPxCHghAByXigYgBfr8LAsYj8aQMUASbDQcRSExCeCwFiIQh+AKfAYyBiQFgOPyIaikSGLQo0Zj-aazaY+dSaXjLDgAGXgAC9CKhDqAALxJaw2Ib2RzOISuDycLw+ImBYKQflCkWRRD2LXCw6JCxS1JCdJZHJ5RAFIbFJU8ADKC3WzEcnVZaGYE1ABpFnFOmsFhsil2uoHuzwArO9SmAAEIsSFrZB-GgAjjA5gtVN8VCEc1o1C4Q4AGlR2AwO1EsBQoAAbvB-gJ4HhPgB5aDwem-Ph1TCV3AEEirTp4ELtRbTPD4vwKjOfAuioSQHuDXBcnmgACC+eCONFEs73YAPGGZVT5cRyyhiHh7AAON7lsG3vBggB8XGV3l8-nVISOgghxoLq9i7io-AHsayRWGaFrlFauq2rg9qaIGQHwCBqChtKdgRo8TxRjeyB3o+7xAA\" rel=\"nofollow\">\u7c7b\u578b\u522b\u540d\u7684\u540d\u5b57\u53ef\u80fd\u4f1a\u51fa\u73b0\u5728\u62a5\u9519\u4fe1\u606f\u4e2d<\/a>\uff0c\u6709\u65f6\u4f1a\u66ff\u4ee3\u7b49\u4ef7\u7684\u533f\u540d\u7c7b\u578b\uff08\u4e5f\u8bb8\u5e76\u4e0d\u662f\u671f\u671b\u7684\uff09\u3002\u63a5\u53e3\u7684\u540d\u5b57\u5219\u4f1a\u59cb\u7ec8\u51fa\u73b0\u5728\u9519\u8bef\u4fe1\u606f\u4e2d\u3002<\/li>\n<li>\u7c7b\u578b\u522b\u540d\u4e5f\u8bb8\u4e0d\u4f1a\u5b9e\u73b0<a href=\"https:\/\/www.typescriptlang.org\/play?#code\/PTAEGEHsFsAcEsA2BTATqNrLusgzngIYDm+oA7koqIYuYQJ56gCueyoAUCKAC4AWHAHaFcoSADMaQ0PCG80EwgGNkALk6c5C1EtWgAsqOi1QAb06groEbjWg8vVHOKcAvpokshy3vEgyyMr8kEbQJogAFND2YREAlOaW1soBeJAoAHSIkMTRmbbI8e6aPMiZxJmgACqCGKhY6ABGyDnkFFQ0dIzMbBwCwqIccabcYLyQoKjIEmh8kwN8DLAc5PzwwbLMyAAeK77IACYaQSEjUWZWhfYAjABMAMwALA+gbsVjoADqgjKESytQPxCHghAByXigYgBfr8LAsYj8aQMUASbDQcRSExCeCwFiIQh+AKfAYyBiQFgOPyIaikSGLQo0Zj-aazaY+dSaXjLDgAGXgAC9CKhDqAALxJaw2Ib2RzOISuDycLw+ImBYKQflCkWRRD2LXCw6JCxS1JCdJZHJ5RAFIbFJU8ADKC3WzEcnVZaGYE1ABpFnFOmsFhsil2uoHuzwArO9SmAAEIsSFrZB-GgAjjA5gtVN8VCEc1o1C4Q4AGlR2AwO1EsBQoAAbvB-gJ4HhPgB5aDwem-Ph1TCV3AEEirTp4ELtRbTPD4vwKjOfAuioSQHuDXBcnmgACC+eCONFEs73YAPGGZVT5cRyyhiHh7AAON7lsG3vBggB8XGV3l8-nVISOgghxoLq9i7io-AHsayRWGaFrlFauq2rg9qaIGQHwCBqChtKdgRo8TxRjeyB3o+7xAA\" rel=\"nofollow\">\u58f0\u660e\u5408\u5e76\uff0c\u4f46\u662f\u63a5\u53e3\u53ef\u4ee5<\/a><\/li>\n<li>\u63a5\u53e3\u53ef\u80fd\u53ea\u4f1a\u88ab\u7528\u4e8e<a href=\"https:\/\/www.typescriptlang.org\/play?#code\/PTAEAkFMCdIcgM6gC4HcD2pIA8CGBbABwBtIl0AzUAKBFAFcEBLAOwHMUBPQs0XFgCahWyGBVwBjMrTDJMAshOhMARpD4tQ6FQCtIE5DWoixk9QEEWAeV37kARlABvaqDegAbrmL1IALlAEZGV2agBfampkbgtrWwMAJlAAXmdXdy8ff0Dg1jZwyLoAVWZ2Lh5QVHUJflAlSFxROsY5fFAWAmk6CnRoLGwmILzQQmV8JmQmDzI-SOiKgGV+CaYAL0gBBdyy1KCQ-Pn1AFFplgA5enw1PtSWS+vCsAAVAAtB4QQWOEMKBuYVUiVCYvYQsUTQcRSBDGMGmKSgAAa-VEgiQe2GLgKQA\" rel=\"nofollow\">\u58f0\u660e\u5bf9\u8c61\u7684\u5f62\u72b6\uff0c\u4e0d\u80fd\u91cd\u547d\u540d\u539f\u59cb\u7c7b\u578b<\/a><\/li>\n<li>\u63a5\u53e3\u901a\u8fc7\u540d\u5b57\u4f7f\u7528\u7684\u65f6\u5019\uff0c\u4ed6\u4eec\u7684\u540d\u5b57\u4f1a<a href=\"https:\/\/www.typescriptlang.org\/play?#code\/PTAEGEHsFsAcEsA2BTATqNrLusgzngIYDm+oA7koqIYuYQJ56gCueyoAUCKAC4AWHAHaFcoSADMaQ0PCG80EwgGNkALk6c5C1EtWgAsqOi1QAb06groEbjWg8vVHOKcAvpokshy3vEgyyMr8kEbQJogAFND2YREAlOaW1soBeJAoAHSIkMTRmbbI8e6aPMiZxJmgACqCGKhY6ABGyDnkFFQ0dIzMbBwCwqIccabcYLyQoKjIEmh8kwN8DLAc5PzwwbLMyAAeK77IACYaQSEjUWY2Q-YAjABMAMwALA+gbsVjNXW8yxySoAADaAA0CCaZbPh1XYqXgOIY0ZgmcK0AA0nyaLFhhGY8F4AHJmEJILCWsgZId4NNfIgGFdcIcUTVfgBlZTOWC8T7kAJ42G4eT+GS42QyRaYbCgXAEEguTzeXyCjDBSAAQSE8Ai0Xsl0K9kcziExDeiQs1lAqSE6SyOTy0AKQ2KHk4p1V6s1OuuoHuzwArMagA\" rel=\"nofollow\">\u603b\u662f\u51fa\u73b0\u5728\u9519\u8bef\u4fe1\u606f\u4e2d\uff0c\u5982\u679c\u76f4\u63a5\u4f7f\u7528\uff0c\u5219\u4f1a\u51fa\u73b0\u539f\u59cb\u7ed3\u6784<\/a><\/li>\n<\/ul>\n<p dir=\"auto\">\u5927\u90e8\u5206\u65f6\u5019\uff0c\u4f60\u53ef\u4ee5\u6839\u636e\u4e2a\u4eba\u559c\u597d\u8fdb\u884c\u9009\u62e9\u3002TypeScript \u4f1a\u544a\u8bc9\u4f60\u5b83\u662f\u5426\u9700\u8981\u5176\u4ed6\u65b9\u5f0f\u7684\u58f0\u660e\u3002\u5982\u679c\u4f60\u559c\u6b22\u63a2\u7d22\u6027\u7684\u4f7f\u7528\uff0c\u90a3\u5c31\u4f7f\u7528 <code class=\"notranslate\">interface<\/code> \uff0c\u76f4\u5230\u4f60\u9700\u8981\u7528\u5230 <code class=\"notranslate\">type<\/code> \u7684\u7279\u6027\u3002<\/p>\n<h2 dir=\"auto\">\u7c7b\u578b\u65ad\u8a00\uff08Type Assertions\uff09<\/h2>\n<p dir=\"auto\">\u6709\u7684\u65f6\u5019\uff0c\u4f60\u77e5\u9053\u4e00\u4e2a\u503c\u7684\u7c7b\u578b\uff0c\u4f46 TypeScript \u4e0d\u77e5\u9053\u3002<\/p>\n<p dir=\"auto\">\u4e3e\u4e2a\u4f8b\u5b50\uff0c\u5982\u679c\u4f60\u4f7f\u7528 <code class=\"notranslate\">document.getElementById<\/code>\uff0cTypeScript \u4ec5\u4ec5\u77e5\u9053\u5b83\u4f1a\u8fd4\u56de\u4e00\u4e2a <code class=\"notranslate\">HTMLElement<\/code>\uff0c\u4f46\u662f\u4f60\u5374\u77e5\u9053\uff0c\u4f60\u8981\u83b7\u53d6\u7684\u662f\u4e00\u4e2a <code class=\"notranslate\">HTMLCanvasElement<\/code>\u3002<\/p>\n<p dir=\"auto\">\u8fd9\u65f6\uff0c\u4f60\u53ef\u4ee5\u4f7f\u7528\u7c7b\u578b\u65ad\u8a00\u5c06\u5176\u6307\u5b9a\u4e3a\u4e00\u4e2a\u66f4\u5177\u4f53\u7684\u7c7b\u578b\uff1a<\/p>\n<div class=\"highlight highlight-source-ts notranslate position-relative overflow-auto\" dir=\"auto\" data-snippet-clipboard-copy-content='const myCanvas = document.getElementById(\"main_canvas\") as HTMLCanvasElement;'>\n<pre class=\"notranslate\"><span class=\"pl-k\">const<\/span> <span class=\"pl-s1\">myCanvas<\/span> <span class=\"pl-c1\">=<\/span> <span class=\"pl-smi\">document<\/span><span class=\"pl-kos\">.<\/span><span class=\"pl-en\">getElementById<\/span><span class=\"pl-kos\">(<\/span><span class=\"pl-s\">\"main_canvas\"<\/span><span class=\"pl-kos\">)<\/span> <span class=\"pl-k\">as<\/span> <span class=\"pl-smi\">HTMLCanvasElement<\/span><span class=\"pl-kos\">;<\/span><\/pre>\n<\/div>\n<p dir=\"auto\">\u5c31\u50cf\u7c7b\u578b\u6ce8\u89e3\u4e00\u6837\uff0c\u7c7b\u578b\u65ad\u8a00\u4e5f\u4f1a\u88ab\u7f16\u8bd1\u5668\u79fb\u9664\uff0c\u5e76\u4e14\u4e0d\u4f1a\u5f71\u54cd\u4efb\u4f55\u8fd0\u884c\u65f6\u7684\u884c\u4e3a\u3002<\/p>\n<p dir=\"auto\">\u4f60\u4e5f\u53ef\u4ee5\u4f7f\u7528\u5c16\u62ec\u53f7\u8bed\u6cd5\uff08\u6ce8\u610f\u4e0d\u80fd\u5728 <code class=\"notranslate\">.tsx<\/code> \u6587\u4ef6\u5185\u4f7f\u7528\uff09\uff0c\u662f\u7b49\u4ef7\u7684\uff1a<\/p>\n<div class=\"highlight highlight-source-ts notranslate position-relative overflow-auto\" dir=\"auto\" data-snippet-clipboard-copy-content='const myCanvas = &lt;HTMLCanvasElement&gt;document.getElementById(\"main_canvas\");'>\n<pre class=\"notranslate\"><span class=\"pl-k\">const<\/span> <span class=\"pl-s1\">myCanvas<\/span> <span class=\"pl-c1\">=<\/span> <span class=\"pl-kos\">&lt;<\/span><span class=\"pl-smi\">HTMLCanvasElement<\/span><span class=\"pl-kos\">&gt;<\/span><span class=\"pl-smi\">document<\/span><span class=\"pl-kos\">.<\/span><span class=\"pl-en\">getElementById<\/span><span class=\"pl-kos\">(<\/span><span class=\"pl-s\">\"main_canvas\"<\/span><span class=\"pl-kos\">)<\/span><span class=\"pl-kos\">;<\/span><\/pre>\n<\/div>\n<blockquote>\n<p dir=\"auto\">\u8c28\u8bb0\uff1a\u56e0\u4e3a\u7c7b\u578b\u65ad\u8a00\u4f1a\u5728\u7f16\u8bd1\u7684\u65f6\u5019\u88ab\u79fb\u9664\uff0c\u6240\u4ee5\u8fd0\u884c\u65f6\u5e76\u4e0d\u4f1a\u6709\u7c7b\u578b\u65ad\u8a00\u7684\u68c0\u67e5\uff0c\u5373\u4f7f\u7c7b\u578b\u65ad\u8a00\u662f\u9519\u8bef\u7684\uff0c\u4e5f\u4e0d\u4f1a\u6709\u5f02\u5e38\u6216\u8005 <code class=\"notranslate\">null<\/code> \u4ea7\u751f\u3002<\/p>\n<\/blockquote>\n<p dir=\"auto\">TypeScript \u4ec5\u4ec5\u5141\u8bb8\u7c7b\u578b\u65ad\u8a00\u8f6c\u6362\u4e3a\u4e00\u4e2a\u66f4\u52a0\u5177\u4f53\u6216\u8005\u66f4\u4e0d\u5177\u4f53\u7684\u7c7b\u578b\u3002\u8fd9\u4e2a\u89c4\u5219\u53ef\u4ee5\u963b\u6b62\u4e00\u4e9b\u4e0d\u53ef\u80fd\u7684\u7c7b\u578b\u6307\u5b9a\uff0c\u6bd4\u5982\uff1a<\/p>\n<div class=\"highlight highlight-source-ts notranslate position-relative overflow-auto\" dir=\"auto\" data-snippet-clipboard-copy-content=\"const x = &quot;hello&quot; as number;\n\/\/ Conversion of type 'string' to type 'number' may be a mistake because neither type sufficiently overlaps with the other. If this was intentional, convert the expression to 'unknown' first.\"><\/p>\n<pre class=\"notranslate\"><span class=\"pl-k\">const<\/span> <span class=\"pl-s1\">x<\/span> <span class=\"pl-c1\">=<\/span> <span class=\"pl-s\">\"hello\"<\/span> <span class=\"pl-k\">as<\/span> <span class=\"pl-smi\">number<\/span><span class=\"pl-kos\">;<\/span>\n<span class=\"pl-c\">\/\/ Conversion of type 'string' to type 'number' may be a mistake because neither type sufficiently overlaps with the other. If this was intentional, convert the expression to 'unknown' first.<\/span><\/pre>\n<\/div>\n<p dir=\"auto\">\u6709\u7684\u65f6\u5019\uff0c\u8fd9\u6761\u89c4\u5219\u4f1a\u663e\u5f97\u975e\u5e38\u4fdd\u5b88\uff0c\u963b\u6b62\u4e86\u4f60\u539f\u672c\u6709\u6548\u7684\u7c7b\u578b\u8f6c\u6362\u3002\u5982\u679c\u53d1\u751f\u4e86\u8fd9\u79cd\u4e8b\u60c5\uff0c\u4f60\u53ef\u4ee5\u4f7f\u7528\u53cc\u91cd\u65ad\u8a00\uff0c\u5148\u65ad\u8a00\u4e3a <code class=\"notranslate\">any<\/code> \uff08\u6216\u8005\u662f <code class=\"notranslate\">unknown<\/code>\uff09\uff0c\u7136\u540e\u518d\u65ad\u8a00\u4e3a\u671f\u671b\u7684\u7c7b\u578b\uff1a<\/p>\n<div class=\"highlight highlight-source-ts notranslate position-relative overflow-auto\" dir=\"auto\" data-snippet-clipboard-copy-content=\"const a = (expr as any) as T;\">\n<pre class=\"notranslate\"><span class=\"pl-k\">const<\/span> <span class=\"pl-s1\">a<\/span> <span class=\"pl-c1\">=<\/span> <span class=\"pl-kos\">(<\/span><span class=\"pl-s1\">expr<\/span> <span class=\"pl-k\">as<\/span> <span class=\"pl-smi\">any<\/span><span class=\"pl-kos\">)<\/span> <span class=\"pl-k\">as<\/span> <span class=\"pl-smi\">T<\/span><span class=\"pl-kos\">;<\/span><\/pre>\n<\/div>\n<h2 dir=\"auto\">\u5b57\u9762\u91cf\u7c7b\u578b\uff08Literal Types\uff09<\/h2>\n<p dir=\"auto\">\u9664\u4e86\u5e38\u89c1\u7684\u7c7b\u578b <code class=\"notranslate\">string<\/code> \u548c <code class=\"notranslate\">number<\/code> \uff0c\u6211\u4eec\u4e5f\u53ef\u4ee5\u5c06\u7c7b\u578b\u58f0\u660e\u4e3a\u66f4\u5177\u4f53\u7684\u6570\u5b57\u6216\u8005\u5b57\u7b26\u4e32\u3002<\/p>\n<p dir=\"auto\">\u4f17\u6240\u5468\u77e5\uff0c\u5728 JavaScript \u4e2d\uff0c\u6709\u591a\u79cd\u65b9\u5f0f\u53ef\u4ee5\u58f0\u660e\u53d8\u91cf\u3002\u6bd4\u5982 <code class=\"notranslate\">var<\/code> \u548c <code class=\"notranslate\">let<\/code> \uff0c\u8fd9\u79cd\u65b9\u5f0f\u58f0\u660e\u7684\u53d8\u91cf\u540e\u7eed\u53ef\u4ee5\u88ab\u4fee\u6539\uff0c\u8fd8\u6709 <code class=\"notranslate\">const<\/code> \uff0c\u8fd9\u79cd\u65b9\u5f0f\u58f0\u660e\u7684\u53d8\u91cf\u5219\u4e0d\u80fd\u88ab\u4fee\u6539\uff0c\u8fd9\u5c31\u4f1a\u5f71\u54cd TypeScript \u4e3a\u5b57\u9762\u91cf\u521b\u5efa\u7c7b\u578b\u3002<\/p>\n<div class=\"highlight highlight-source-ts notranslate position-relative overflow-auto\" dir=\"auto\" data-snippet-clipboard-copy-content='let changingString = \"Hello World\";\nchangingString = \"Ol\u00e1 Mundo\";\n\/\/ Because `changingString` can represent any possible string, that\n\/\/ is how TypeScript describes it in the type system\nchangingString;\n\/\/ let changingString: string'><\/p>\n<pre class=\"notranslate\"><span class=\"pl-k\">let<\/span> <span class=\"pl-s1\">changingString<\/span> <span class=\"pl-c1\">=<\/span> <span class=\"pl-s\">\"Hello World\"<\/span><span class=\"pl-kos\">;<\/span>\n<span class=\"pl-s1\">changingString<\/span> <span class=\"pl-c1\">=<\/span> <span class=\"pl-s\">\"Ol\u00e1 Mundo\"<\/span><span class=\"pl-kos\">;<\/span>\n<span class=\"pl-c\">\/\/ Because `changingString` can represent any possible string, that<\/span>\n<span class=\"pl-c\">\/\/ is how TypeScript describes it in the type system<\/span>\n<span class=\"pl-s1\">changingString<\/span><span class=\"pl-kos\">;<\/span>\n<span class=\"pl-c\">\/\/ let changingString: string<\/span><\/pre>\n<\/div>\n<div class=\"highlight highlight-source-ts notranslate position-relative overflow-auto\" dir=\"auto\" data-snippet-clipboard-copy-content='const constantString = \"Hello World\";\n\/\/ Because `constantString` can only represent 1 possible string, it\n\/\/ has a literal type representation\nconstantString;\n\/\/ const constantString: \"Hello World\"'><\/p>\n<pre class=\"notranslate\"><span class=\"pl-k\">const<\/span> <span class=\"pl-s1\">constantString<\/span> <span class=\"pl-c1\">=<\/span> <span class=\"pl-s\">\"Hello World\"<\/span><span class=\"pl-kos\">;<\/span>\n<span class=\"pl-c\">\/\/ Because `constantString` can only represent 1 possible string, it<\/span>\n<span class=\"pl-c\">\/\/ has a literal type representation<\/span>\n<span class=\"pl-s1\">constantString<\/span><span class=\"pl-kos\">;<\/span>\n<span class=\"pl-c\">\/\/ const constantString: \"Hello World\"<\/span><\/pre>\n<\/div>\n<p dir=\"auto\">\u5b57\u9762\u91cf\u7c7b\u578b\u672c\u8eab\u5e76\u6ca1\u6709\u4ec0\u4e48\u592a\u5927\u7528\uff1a<\/p>\n<div class=\"highlight highlight-source-ts notranslate position-relative overflow-auto\" dir=\"auto\" data-snippet-clipboard-copy-content=\"let x: &quot;hello&quot; = &quot;hello&quot;;\n\/\/ OK\nx = &quot;hello&quot;;\n\/\/ ...\nx = &quot;howdy&quot;;\n\/\/ Type '&quot;howdy&quot;' is not assignable to type '&quot;hello&quot;'.\"><\/p>\n<pre class=\"notranslate\"><span class=\"pl-k\">let<\/span> <span class=\"pl-s1\">x<\/span>: <span class=\"pl-s\">\"hello\"<\/span> <span class=\"pl-c1\">=<\/span> <span class=\"pl-s\">\"hello\"<\/span><span class=\"pl-kos\">;<\/span>\n<span class=\"pl-c\">\/\/ OK<\/span>\n<span class=\"pl-s1\">x<\/span> <span class=\"pl-c1\">=<\/span> <span class=\"pl-s\">\"hello\"<\/span><span class=\"pl-kos\">;<\/span>\n<span class=\"pl-c\">\/\/ ...<\/span>\n<span class=\"pl-s1\">x<\/span> <span class=\"pl-c1\">=<\/span> <span class=\"pl-s\">\"howdy\"<\/span><span class=\"pl-kos\">;<\/span>\n<span class=\"pl-c\">\/\/ Type '\"howdy\"' is not assignable to type '\"hello\"'.<\/span><\/pre>\n<\/div>\n<p dir=\"auto\">\u5982\u679c\u7ed3\u5408\u8054\u5408\u7c7b\u578b\uff0c\u5c31\u663e\u5f97\u6709\u7528\u591a\u4e86\u3002\u4e3e\u4e2a\u4f8b\u5b50\uff0c\u5f53\u51fd\u6570\u53ea\u80fd\u4f20\u5165\u4e00\u4e9b\u56fa\u5b9a\u7684\u5b57\u7b26\u4e32\u65f6\uff1a<\/p>\n<div class=\"highlight highlight-source-ts notranslate position-relative overflow-auto\" dir=\"auto\" data-snippet-clipboard-copy-content=\"function printText(s: string, alignment: &quot;left&quot; | &quot;right&quot; | &quot;center&quot;) {\n  \/\/ ...\n}\nprintText(&quot;Hello, world&quot;, &quot;left&quot;);\nprintText(&quot;G'day, mate&quot;, &quot;centre&quot;);\n\/\/ Argument of type '&quot;centre&quot;' is not assignable to parameter of type '&quot;left&quot; | &quot;right&quot; | &quot;center&quot;'.\"><\/p>\n<pre class=\"notranslate\"><span class=\"pl-k\">function<\/span> <span class=\"pl-en\">printText<\/span><span class=\"pl-kos\">(<\/span><span class=\"pl-s1\">s<\/span>: <span class=\"pl-smi\">string<\/span><span class=\"pl-kos\">,<\/span> <span class=\"pl-s1\">alignment<\/span>: <span class=\"pl-s\">\"left\"<\/span> <span class=\"pl-c1\">|<\/span> <span class=\"pl-s\">\"right\"<\/span> <span class=\"pl-c1\">|<\/span> <span class=\"pl-s\">\"center\"<\/span><span class=\"pl-kos\">)<\/span> <span class=\"pl-kos\">{<\/span>\n  <span class=\"pl-c\">\/\/ ...<\/span>\n<span class=\"pl-kos\">}<\/span>\n<span class=\"pl-en\">printText<\/span><span class=\"pl-kos\">(<\/span><span class=\"pl-s\">\"Hello, world\"<\/span><span class=\"pl-kos\">,<\/span> <span class=\"pl-s\">\"left\"<\/span><span class=\"pl-kos\">)<\/span><span class=\"pl-kos\">;<\/span>\n<span class=\"pl-en\">printText<\/span><span class=\"pl-kos\">(<\/span><span class=\"pl-s\">\"G'day, mate\"<\/span><span class=\"pl-kos\">,<\/span> <span class=\"pl-s\">\"centre\"<\/span><span class=\"pl-kos\">)<\/span><span class=\"pl-kos\">;<\/span>\n<span class=\"pl-c\">\/\/ Argument of type '\"centre\"' is not assignable to parameter of type '\"left\" | \"right\" | \"center\"'.<\/span><\/pre>\n<\/div>\n<p dir=\"auto\">\u6570\u5b57\u5b57\u9762\u91cf\u7c7b\u578b\u4e5f\u662f\u4e00\u6837\u7684\uff1a<\/p>\n<div class=\"highlight highlight-source-ts notranslate position-relative overflow-auto\" dir=\"auto\" data-snippet-clipboard-copy-content=\"function compare(a: string, b: string): -1 | 0 | 1 {\n  return a === b ? 0 : a &gt; b ? 1 : -1;\n}\"><\/p>\n<pre class=\"notranslate\"><span class=\"pl-k\">function<\/span> <span class=\"pl-en\">compare<\/span><span class=\"pl-kos\">(<\/span><span class=\"pl-s1\">a<\/span>: <span class=\"pl-smi\">string<\/span><span class=\"pl-kos\">,<\/span> <span class=\"pl-s1\">b<\/span>: <span class=\"pl-smi\">string<\/span><span class=\"pl-kos\">)<\/span>: <span class=\"pl-c1\">-<\/span><span class=\"pl-c1\">1<\/span> <span class=\"pl-c1\">|<\/span> <span class=\"pl-c1\">0<\/span> <span class=\"pl-c1\">|<\/span> <span class=\"pl-c1\">1<\/span> <span class=\"pl-kos\">{<\/span>\n  <span class=\"pl-k\">return<\/span> <span class=\"pl-s1\">a<\/span> <span class=\"pl-c1\">===<\/span> <span class=\"pl-s1\">b<\/span> ? <span class=\"pl-c1\">0<\/span> : <span class=\"pl-s1\">a<\/span> <span class=\"pl-c1\">&gt;<\/span> <span class=\"pl-s1\">b<\/span> ? <span class=\"pl-c1\">1<\/span> : <span class=\"pl-c1\">-<\/span><span class=\"pl-c1\">1<\/span><span class=\"pl-kos\">;<\/span>\n<span class=\"pl-kos\">}<\/span><\/pre>\n<\/div>\n<p dir=\"auto\">\u5f53\u7136\u4e86\uff0c\u4f60\u4e5f\u53ef\u4ee5\u8ddf\u975e\u5b57\u9762\u91cf\u7c7b\u578b\u8054\u5408\uff1a<\/p>\n<div class=\"highlight highlight-source-ts notranslate position-relative overflow-auto\" dir=\"auto\" data-snippet-clipboard-copy-content=\"interface Options {\n  width: number;\n}\nfunction configure(x: Options | &quot;auto&quot;) {\n  \/\/ ...\n}\nconfigure({ width: 100 });\nconfigure(&quot;auto&quot;);\nconfigure(&quot;automatic&quot;);\n\n\/\/ Argument of type '&quot;automatic&quot;' is not assignable to parameter of type 'Options | &quot;auto&quot;'.\"><\/p>\n<pre class=\"notranslate\"><span class=\"pl-k\">interface<\/span> <span class=\"pl-smi\">Options<\/span> <span class=\"pl-kos\">{<\/span>\n  <span class=\"pl-c1\">width<\/span>: <span class=\"pl-smi\">number<\/span><span class=\"pl-kos\">;<\/span>\n<span class=\"pl-kos\">}<\/span>\n<span class=\"pl-k\">function<\/span> <span class=\"pl-en\">configure<\/span><span class=\"pl-kos\">(<\/span><span class=\"pl-s1\">x<\/span>: <span class=\"pl-smi\">Options<\/span> <span class=\"pl-c1\">|<\/span> <span class=\"pl-s\">\"auto\"<\/span><span class=\"pl-kos\">)<\/span> <span class=\"pl-kos\">{<\/span>\n  <span class=\"pl-c\">\/\/ ...<\/span>\n<span class=\"pl-kos\">}<\/span>\n<span class=\"pl-en\">configure<\/span><span class=\"pl-kos\">(<\/span><span class=\"pl-kos\">{<\/span> <span class=\"pl-c1\">width<\/span>: <span class=\"pl-c1\">100<\/span> <span class=\"pl-kos\">}<\/span><span class=\"pl-kos\">)<\/span><span class=\"pl-kos\">;<\/span>\n<span class=\"pl-en\">configure<\/span><span class=\"pl-kos\">(<\/span><span class=\"pl-s\">\"auto\"<\/span><span class=\"pl-kos\">)<\/span><span class=\"pl-kos\">;<\/span>\n<span class=\"pl-en\">configure<\/span><span class=\"pl-kos\">(<\/span><span class=\"pl-s\">\"automatic\"<\/span><span class=\"pl-kos\">)<\/span><span class=\"pl-kos\">;<\/span>\n\n<span class=\"pl-c\">\/\/ Argument of type '\"automatic\"' is not assignable to parameter of type 'Options | \"auto\"'.<\/span><\/pre>\n<\/div>\n<p dir=\"auto\">\u8fd8\u6709\u4e00\u79cd\u5b57\u9762\u91cf\u7c7b\u578b\uff0c\u5e03\u5c14\u5b57\u9762\u91cf\u3002\u56e0\u4e3a\u53ea\u6709\u4e24\u79cd\u5e03\u5c14\u5b57\u9762\u91cf\u7c7b\u578b\uff0c <code class=\"notranslate\">true<\/code> \u548c <code class=\"notranslate\">false<\/code> \uff0c\u7c7b\u578b <code class=\"notranslate\">boolean<\/code> \u5b9e\u9645\u4e0a\u5c31\u662f\u8054\u5408\u7c7b\u578b <code class=\"notranslate\">true | false<\/code> \u7684\u522b\u540d\u3002<\/p>\n<h3 dir=\"auto\">\u5b57\u9762\u91cf\u63a8\u65ad\uff08Literal Inference\uff09<\/h3>\n<p dir=\"auto\">\u5f53\u4f60\u521d\u59cb\u5316\u53d8\u91cf\u4e3a\u4e00\u4e2a\u5bf9\u8c61\u7684\u65f6\u5019\uff0cTypeScript \u4f1a\u5047\u8bbe\u8fd9\u4e2a\u5bf9\u8c61\u7684\u5c5e\u6027\u7684\u503c\u672a\u6765\u4f1a\u88ab\u4fee\u6539\uff0c\u4e3e\u4e2a\u4f8b\u5b50\uff0c\u5982\u679c\u4f60\u5199\u4e0b\u8fd9\u6837\u7684\u4ee3\u7801\uff1a<\/p>\n<div class=\"highlight highlight-source-ts notranslate position-relative overflow-auto\" dir=\"auto\" data-snippet-clipboard-copy-content=\"const obj = { counter: 0 };\nif (someCondition) {\n  obj.counter = 1;\n}\"><\/p>\n<pre class=\"notranslate\"><span class=\"pl-k\">const<\/span> <span class=\"pl-s1\">obj<\/span> <span class=\"pl-c1\">=<\/span> <span class=\"pl-kos\">{<\/span> <span class=\"pl-c1\">counter<\/span>: <span class=\"pl-c1\">0<\/span> <span class=\"pl-kos\">}<\/span><span class=\"pl-kos\">;<\/span>\n<span class=\"pl-k\">if<\/span> <span class=\"pl-kos\">(<\/span><span class=\"pl-s1\">someCondition<\/span><span class=\"pl-kos\">)<\/span> <span class=\"pl-kos\">{<\/span>\n  <span class=\"pl-s1\">obj<\/span><span class=\"pl-kos\">.<\/span><span class=\"pl-c1\">counter<\/span> <span class=\"pl-c1\">=<\/span> <span class=\"pl-c1\">1<\/span><span class=\"pl-kos\">;<\/span>\n<span class=\"pl-kos\">}<\/span><\/pre>\n<\/div>\n<p dir=\"auto\">TypeScript \u5e76\u4e0d\u4f1a\u8ba4\u4e3a <code class=\"notranslate\">obj.counter<\/code> \u4e4b\u524d\u662f <code class=\"notranslate\">0<\/code>\uff0c \u73b0\u5728\u88ab\u8d4b\u503c\u4e3a <code class=\"notranslate\">1<\/code> \u662f\u4e00\u4e2a\u9519\u8bef\u3002\u6362\u53e5\u8bdd\u8bf4\uff0c<code class=\"notranslate\">obj.counter<\/code> \u5fc5\u987b\u662f <code class=\"notranslate\">number<\/code> \u7c7b\u578b\uff0c\u4f46\u4e0d\u8981\u6c42\u4e00\u5b9a\u662f <code class=\"notranslate\">0<\/code>\uff0c\u56e0\u4e3a\u7c7b\u578b\u53ef\u4ee5\u51b3\u5b9a\u8bfb\u5199\u884c\u4e3a\u3002<\/p>\n<p dir=\"auto\">\u8fd9\u4e5f\u540c\u6837\u5e94\u7528\u4e8e\u5b57\u7b26\u4e32:<\/p>\n<div class=\"highlight highlight-source-ts notranslate position-relative overflow-auto\" dir=\"auto\" data-snippet-clipboard-copy-content=\"declare function handleRequest(url: string, method: &quot;GET&quot; | &quot;POST&quot;): void;\n\nconst req = { url: &quot;https:\/\/example.com&quot;, method: &quot;GET&quot; };\nhandleRequest(req.url, req.method);\n\n\/\/ Argument of type 'string' is not assignable to parameter of type '&quot;GET&quot; | &quot;POST&quot;'.\"><\/p>\n<pre class=\"notranslate\"><span class=\"pl-k\">declare<\/span> <span class=\"pl-k\">function<\/span> <span class=\"pl-s1\">handleRequest<\/span><span class=\"pl-kos\">(<\/span><span class=\"pl-s1\">url<\/span>: <span class=\"pl-smi\">string<\/span><span class=\"pl-kos\">,<\/span> <span class=\"pl-s1\">method<\/span>: <span class=\"pl-s\">\"GET\"<\/span> <span class=\"pl-c1\">|<\/span> <span class=\"pl-s\">\"POST\"<\/span><span class=\"pl-kos\">)<\/span>: <span class=\"pl-smi\"><span class=\"pl-k\">void<\/span><\/span><span class=\"pl-kos\">;<\/span>\n\n<span class=\"pl-k\">const<\/span> <span class=\"pl-s1\">req<\/span> <span class=\"pl-c1\">=<\/span> <span class=\"pl-kos\">{<\/span> <span class=\"pl-c1\">url<\/span>: <span class=\"pl-s\">\"https:\/\/example.com\"<\/span><span class=\"pl-kos\">,<\/span> <span class=\"pl-c1\">method<\/span>: <span class=\"pl-s\">\"GET\"<\/span> <span class=\"pl-kos\">}<\/span><span class=\"pl-kos\">;<\/span>\n<span class=\"pl-en\">handleRequest<\/span><span class=\"pl-kos\">(<\/span><span class=\"pl-s1\">req<\/span><span class=\"pl-kos\">.<\/span><span class=\"pl-c1\">url<\/span><span class=\"pl-kos\">,<\/span> <span class=\"pl-s1\">req<\/span><span class=\"pl-kos\">.<\/span><span class=\"pl-c1\">method<\/span><span class=\"pl-kos\">)<\/span><span class=\"pl-kos\">;<\/span>\n\n<span class=\"pl-c\">\/\/ Argument of type 'string' is not assignable to parameter of type '\"GET\" | \"POST\"'.<\/span><\/pre>\n<\/div>\n<p dir=\"auto\">\u5728\u4e0a\u9762\u8fd9\u4e2a\u4f8b\u5b50\u91cc\uff0c<code class=\"notranslate\">req.method<\/code> \u88ab\u63a8\u65ad\u4e3a <code class=\"notranslate\">string<\/code> \uff0c\u800c\u4e0d\u662f <code class=\"notranslate\">\"GET\"<\/code>\uff0c\u56e0\u4e3a\u5728\u521b\u5efa <code class=\"notranslate\">req<\/code> \u548c \u8c03\u7528 <code class=\"notranslate\">handleRequest<\/code> \u51fd\u6570\u4e4b\u95f4\uff0c\u53ef\u80fd\u8fd8\u6709\u5176\u4ed6\u7684\u4ee3\u7801\uff0c\u6216\u8bb8\u4f1a\u5c06 <code class=\"notranslate\">req.method<\/code> \u8d4b\u503c\u4e00\u4e2a\u65b0\u5b57\u7b26\u4e32\u6bd4\u5982 <code class=\"notranslate\">\"Guess\"<\/code> \u3002\u6240\u4ee5 TypeScript \u5c31\u62a5\u9519\u4e86\u3002<\/p>\n<p dir=\"auto\">\u6709\u4e24\u79cd\u65b9\u5f0f\u53ef\u4ee5\u89e3\u51b3\uff1a<\/p>\n<ol dir=\"auto\">\n<li>\u6dfb\u52a0\u4e00\u4e2a\u7c7b\u578b\u65ad\u8a00\u6539\u53d8\u63a8\u65ad\u7ed3\u679c\uff1a<\/li>\n<\/ol>\n<div class=\"highlight highlight-source-ts notranslate position-relative overflow-auto\" dir=\"auto\" data-snippet-clipboard-copy-content='\/\/ Change 1:\nconst req = { url: \"https:\/\/example.com\", method: \"GET\" as \"GET\" };\n\/\/ Change 2\nhandleRequest(req.url, req.method as \"GET\");'><\/p>\n<pre class=\"notranslate\"><span class=\"pl-c\">\/\/ Change 1:<\/span>\n<span class=\"pl-k\">const<\/span> <span class=\"pl-s1\">req<\/span> <span class=\"pl-c1\">=<\/span> <span class=\"pl-kos\">{<\/span> <span class=\"pl-c1\">url<\/span>: <span class=\"pl-s\">\"https:\/\/example.com\"<\/span><span class=\"pl-kos\">,<\/span> <span class=\"pl-c1\">method<\/span>: <span class=\"pl-s\">\"GET\"<\/span> <span class=\"pl-k\">as<\/span> <span class=\"pl-s\">\"GET\"<\/span> <span class=\"pl-kos\">}<\/span><span class=\"pl-kos\">;<\/span>\n<span class=\"pl-c\">\/\/ Change 2<\/span>\n<span class=\"pl-en\">handleRequest<\/span><span class=\"pl-kos\">(<\/span><span class=\"pl-s1\">req<\/span><span class=\"pl-kos\">.<\/span><span class=\"pl-c1\">url<\/span><span class=\"pl-kos\">,<\/span> <span class=\"pl-s1\">req<\/span><span class=\"pl-kos\">.<\/span><span class=\"pl-c1\">method<\/span> <span class=\"pl-k\">as<\/span> <span class=\"pl-s\">\"GET\"<\/span><span class=\"pl-kos\">)<\/span><span class=\"pl-kos\">;<\/span><\/pre>\n<\/div>\n<p dir=\"auto\">\u4fee\u6539 1 \u8868\u793a\u201c\u6211\u6709\u610f\u8ba9 <code class=\"notranslate\">req.method<\/code> \u7684\u7c7b\u578b\u4e3a\u5b57\u9762\u91cf\u7c7b\u578b <code class=\"notranslate\">\"GET\"<\/code>\uff0c\u8fd9\u4f1a\u963b\u6b62\u672a\u6765\u53ef\u80fd\u8d4b\u503c\u4e3a <code class=\"notranslate\">\"GUESS\"<\/code> \u7b49\u5b57\u6bb5\u201d\u3002\u4fee\u6539 2 \u8868\u793a\u201c\u6211\u77e5\u9053 <code class=\"notranslate\">req.method<\/code> \u7684\u503c\u662f <code class=\"notranslate\">\"GET\"<\/code>\u201d.<\/p>\n<ol start=\"2\" dir=\"auto\">\n<li>\u4f60\u4e5f\u53ef\u4ee5\u4f7f\u7528 <code class=\"notranslate\">as const<\/code> \u628a\u6574\u4e2a\u5bf9\u8c61\u8f6c\u4e3a\u4e00\u4e2a\u7c7b\u578b\u5b57\u9762\u91cf\uff1a<\/li>\n<\/ol>\n<div class=\"highlight highlight-source-ts notranslate position-relative overflow-auto\" dir=\"auto\" data-snippet-clipboard-copy-content='const req = { url: \"https:\/\/example.com\", method: \"GET\" } as const;\nhandleRequest(req.url, req.method);'><\/p>\n<pre class=\"notranslate\"><span class=\"pl-k\">const<\/span> <span class=\"pl-s1\">req<\/span> <span class=\"pl-c1\">=<\/span> <span class=\"pl-kos\">{<\/span> <span class=\"pl-c1\">url<\/span>: <span class=\"pl-s\">\"https:\/\/example.com\"<\/span><span class=\"pl-kos\">,<\/span> <span class=\"pl-c1\">method<\/span>: <span class=\"pl-s\">\"GET\"<\/span> <span class=\"pl-kos\">}<\/span> <span class=\"pl-k\">as<\/span> <span class=\"pl-smi\">const<\/span><span class=\"pl-kos\">;<\/span>\n<span class=\"pl-en\">handleRequest<\/span><span class=\"pl-kos\">(<\/span><span class=\"pl-s1\">req<\/span><span class=\"pl-kos\">.<\/span><span class=\"pl-c1\">url<\/span><span class=\"pl-kos\">,<\/span> <span class=\"pl-s1\">req<\/span><span class=\"pl-kos\">.<\/span><span class=\"pl-c1\">method<\/span><span class=\"pl-kos\">)<\/span><span class=\"pl-kos\">;<\/span><\/pre>\n<\/div>\n<p dir=\"auto\"><code class=\"notranslate\">as const<\/code> \u6548\u679c\u8ddf <code class=\"notranslate\">const<\/code> \u7c7b\u4f3c\uff0c\u4f46\u662f\u5bf9\u7c7b\u578b\u7cfb\u7edf\u800c\u8a00\uff0c\u5b83\u53ef\u4ee5\u786e\u4fdd\u6240\u6709\u7684\u5c5e\u6027\u90fd\u88ab\u8d4b\u4e88\u4e00\u4e2a\u5b57\u9762\u91cf\u7c7b\u578b\uff0c\u800c\u4e0d\u662f\u4e00\u4e2a\u66f4\u901a\u7528\u7684\u7c7b\u578b\u6bd4\u5982 <code class=\"notranslate\">string<\/code> \u6216\u8005 <code class=\"notranslate\">number<\/code> \u3002<\/p>\n<h2 dir=\"auto\"><code class=\"notranslate\">null<\/code> \u548c <code class=\"notranslate\">undefined<\/code><\/h2>\n<p dir=\"auto\">JavaScript \u6709\u4e24\u4e2a\u539f\u59cb\u7c7b\u578b\u7684\u503c\uff0c\u7528\u4e8e\u8868\u793a\u7a7a\u7f3a\u6216\u8005\u672a\u521d\u59cb\u5316\uff0c\u4ed6\u4eec\u5206\u522b\u662f <code class=\"notranslate\">null<\/code> \u548c <code class=\"notranslate\">undefined<\/code> \u3002<\/p>\n<p dir=\"auto\">TypeScript \u6709\u4e24\u4e2a\u5bf9\u5e94\u7684\u540c\u540d\u7c7b\u578b\u3002\u5b83\u4eec\u7684\u884c\u4e3a\u53d6\u51b3\u4e8e\u662f\u5426\u6253\u5f00\u4e86 <a href=\"https:\/\/www.typescriptlang.org\/tsconfig#strictNullChecks\" rel=\"nofollow\">strictNullChecks<\/a> \u9009\u9879\u3002<\/p>\n<h3 dir=\"auto\"><code class=\"notranslate\">strictNullChecks<\/code> \u5173\u95ed<\/h3>\n<p dir=\"auto\">\u5f53 <a href=\"https:\/\/www.typescriptlang.org\/tsconfig#strictNullChecks\" rel=\"nofollow\">strictNullChecks<\/a> \u9009\u9879\u5173\u95ed\u7684\u65f6\u5019\uff0c\u5982\u679c\u4e00\u4e2a\u503c\u53ef\u80fd\u662f <code class=\"notranslate\">null<\/code> \u6216\u8005 <code class=\"notranslate\">undefined<\/code>\uff0c\u5b83\u4f9d\u7136\u53ef\u4ee5\u88ab\u6b63\u786e\u7684\u8bbf\u95ee\uff0c\u6216\u8005\u88ab\u8d4b\u503c\u7ed9\u4efb\u610f\u7c7b\u578b\u7684\u5c5e\u6027\u3002\u8fd9\u6709\u70b9\u7c7b\u4f3c\u4e8e\u6ca1\u6709\u7a7a\u503c\u68c0\u67e5\u7684\u8bed\u8a00 (\u6bd4\u5982 C# \uff0cJava) \u3002\u8fd9\u4e9b\u68c0\u67e5\u7684\u7f3a\u5c11\uff0c\u662f\u5bfc\u81f4 bug \u7684\u4e3b\u8981\u6e90\u5934\uff0c\u6240\u4ee5\u6211\u4eec\u59cb\u7ec8\u63a8\u8350\u5f00\u53d1\u8005\u5f00\u542f <a href=\"https:\/\/www.typescriptlang.org\/tsconfig#strictNullChecks\" rel=\"nofollow\">strictNullChecks<\/a> \u9009\u9879\u3002<\/p>\n<h3 dir=\"auto\"><code class=\"notranslate\">strictNullChecks<\/code> \u6253\u5f00<\/h3>\n<p dir=\"auto\">\u5f53 <a href=\"https:\/\/www.typescriptlang.org\/tsconfig#strictNullChecks\" rel=\"nofollow\">strictNullChecks<\/a> \u9009\u9879\u6253\u5f00\u7684\u65f6\u5019\uff0c\u5982\u679c\u4e00\u4e2a\u503c\u53ef\u80fd\u662f <code class=\"notranslate\">null<\/code> \u6216\u8005 <code class=\"notranslate\">undefined<\/code>\uff0c\u4f60\u9700\u8981\u5728\u7528\u5b83\u7684\u65b9\u6cd5\u6216\u8005\u5c5e\u6027\u4e4b\u524d\uff0c\u5148\u68c0\u67e5\u8fd9\u4e9b\u503c\uff0c\u5c31\u50cf\u7528\u53ef\u9009\u7684\u5c5e\u6027\u4e4b\u524d\uff0c\u5148\u68c0\u67e5\u4e00\u4e0b \u662f\u5426\u662f <code class=\"notranslate\">undefined<\/code> \uff0c\u6211\u4eec\u4e5f\u53ef\u4ee5\u4f7f\u7528\u7c7b\u578b\u6536\u7a84\uff08narrowing\uff09\u68c0\u67e5\u503c\u662f\u5426\u662f <code class=\"notranslate\">null<\/code>\uff1a<\/p>\n<div class=\"highlight highlight-source-ts notranslate position-relative overflow-auto\" dir=\"auto\" data-snippet-clipboard-copy-content='function doSomething(x: string | null) {\n  if (x === null) {\n    \/\/ do nothing\n  } else {\n    console.log(\"Hello, \" + x.toUpperCase());\n  }\n}'><\/p>\n<pre class=\"notranslate\"><span class=\"pl-k\">function<\/span> <span class=\"pl-en\">doSomething<\/span><span class=\"pl-kos\">(<\/span><span class=\"pl-s1\">x<\/span>: <span class=\"pl-smi\">string<\/span> <span class=\"pl-c1\">|<\/span> <span class=\"pl-c1\">null<\/span><span class=\"pl-kos\">)<\/span> <span class=\"pl-kos\">{<\/span>\n  <span class=\"pl-k\">if<\/span> <span class=\"pl-kos\">(<\/span><span class=\"pl-s1\">x<\/span> <span class=\"pl-c1\">===<\/span> <span class=\"pl-c1\">null<\/span><span class=\"pl-kos\">)<\/span> <span class=\"pl-kos\">{<\/span>\n    <span class=\"pl-c\">\/\/ do nothing<\/span>\n  <span class=\"pl-kos\">}<\/span> <span class=\"pl-k\">else<\/span> <span class=\"pl-kos\">{<\/span>\n    <span class=\"pl-smi\">console<\/span><span class=\"pl-kos\">.<\/span><span class=\"pl-en\">log<\/span><span class=\"pl-kos\">(<\/span><span class=\"pl-s\">\"Hello, \"<\/span> <span class=\"pl-c1\">+<\/span> <span class=\"pl-s1\">x<\/span><span class=\"pl-kos\">.<\/span><span class=\"pl-en\">toUpperCase<\/span><span class=\"pl-kos\">(<\/span><span class=\"pl-kos\">)<\/span><span class=\"pl-kos\">)<\/span><span class=\"pl-kos\">;<\/span>\n  <span class=\"pl-kos\">}<\/span>\n<span class=\"pl-kos\">}<\/span><\/pre>\n<\/div>\n<h2 dir=\"auto\">\u975e\u7a7a\u65ad\u8a00\u64cd\u4f5c\u7b26\uff08\u540e\u7f00 <code class=\"notranslate\">!<\/code>\uff09(Non-null Assertion Operator)<\/h2>\n<p dir=\"auto\">TypeScript \u63d0\u4f9b\u4e86\u4e00\u4e2a\u7279\u6b8a\u7684\u8bed\u6cd5\uff0c\u53ef\u4ee5\u5728\u4e0d\u505a\u4efb\u4f55\u68c0\u67e5\u7684\u60c5\u51b5\u4e0b\uff0c\u4ece\u7c7b\u578b\u4e2d\u79fb\u9664 <code class=\"notranslate\">null<\/code> \u548c <code class=\"notranslate\">undefined<\/code>\uff0c\u8fd9\u5c31\u662f\u5728\u4efb\u610f\u8868\u8fbe\u5f0f\u540e\u9762\u5199\u4e0a <code class=\"notranslate\">!<\/code>  \uff0c\u8fd9\u662f\u4e00\u4e2a\u6709\u6548\u7684\u7c7b\u578b\u65ad\u8a00\uff0c\u8868\u793a\u5b83\u7684\u503c\u4e0d\u53ef\u80fd\u662f <code class=\"notranslate\">null<\/code> \u6216\u8005 <code class=\"notranslate\">undefined<\/code>\uff1a<\/p>\n<div class=\"highlight highlight-source-ts notranslate position-relative overflow-auto\" dir=\"auto\" data-snippet-clipboard-copy-content=\"function liveDangerously(x?: number | null) {\n  \/\/ No error\n  console.log(x!.toFixed());\n}\"><\/p>\n<pre class=\"notranslate\"><span class=\"pl-k\">function<\/span> <span class=\"pl-en\">liveDangerously<\/span><span class=\"pl-kos\">(<\/span><span class=\"pl-s1\">x<\/span>?: <span class=\"pl-smi\">number<\/span> <span class=\"pl-c1\">|<\/span> <span class=\"pl-c1\">null<\/span><span class=\"pl-kos\">)<\/span> <span class=\"pl-kos\">{<\/span>\n  <span class=\"pl-c\">\/\/ No error<\/span>\n  <span class=\"pl-smi\">console<\/span><span class=\"pl-kos\">.<\/span><span class=\"pl-en\">log<\/span><span class=\"pl-kos\">(<\/span><span class=\"pl-s1\">x<\/span><span class=\"pl-c1\">!<\/span><span class=\"pl-kos\">.<\/span><span class=\"pl-en\">toFixed<\/span><span class=\"pl-kos\">(<\/span><span class=\"pl-kos\">)<\/span><span class=\"pl-kos\">)<\/span><span class=\"pl-kos\">;<\/span>\n<span class=\"pl-kos\">}<\/span><\/pre>\n<\/div>\n<p dir=\"auto\">\u5c31\u50cf\u5176\u4ed6\u7684\u7c7b\u578b\u65ad\u8a00\uff0c\u8fd9\u4e5f\u4e0d\u4f1a\u66f4\u6539\u4efb\u4f55\u8fd0\u884c\u65f6\u7684\u884c\u4e3a\u3002\u91cd\u8981\u7684\u4e8b\u60c5\u8bf4\u4e00\u904d\uff0c\u53ea\u6709\u5f53\u4f60\u660e\u786e\u7684\u77e5\u9053\u8fd9\u4e2a\u503c\u4e0d\u53ef\u80fd\u662f <code class=\"notranslate\">null<\/code> \u6216\u8005 <code class=\"notranslate\">undefined<\/code> \u65f6\u624d\u4f7f\u7528 <code class=\"notranslate\">!<\/code> \u3002<\/p>\n<h2 dir=\"auto\">\u679a\u4e3e\uff08Enums\uff09<\/h2>\n<p dir=\"auto\">\u679a\u4e3e\u662f TypeScript \u6dfb\u52a0\u7684\u65b0\u7279\u6027\uff0c\u7528\u4e8e\u63cf\u8ff0\u4e00\u4e2a\u503c\u53ef\u80fd\u662f\u591a\u4e2a\u5e38\u91cf\u4e2d\u7684\u4e00\u4e2a\u3002\u4e0d\u540c\u4e8e\u5927\u90e8\u5206\u7684 TypeScript \u7279\u6027\uff0c\u8fd9\u5e76\u4e0d\u662f\u4e00\u4e2a\u7c7b\u578b\u5c42\u9762\u7684\u589e\u91cf\uff0c\u800c\u662f\u4f1a\u6dfb\u52a0\u5230\u8bed\u8a00\u548c\u8fd0\u884c\u65f6\u3002\u56e0\u4e3a\u5982\u6b64\uff0c\u4f60\u5e94\u8be5\u4e86\u89e3\u4e0b\u8fd9\u4e2a\u7279\u6027\u3002\u4f46\u662f\u53ef\u4ee5\u7b49\u4e00\u7b49\u518d\u7528\uff0c\u9664\u975e\u4f60\u786e\u5b9a\u8981\u4f7f\u7528\u5b83\u3002\u4f60\u53ef\u4ee5\u5728<a href=\"https:\/\/www.typescriptlang.org\/docs\/handbook\/enums.html\" rel=\"nofollow\">\u679a\u4e3e\u7c7b\u578b<\/a>\u9875\u9762\u4e86\u89e3\u66f4\u591a\u7684\u4fe1\u606f\u3002<\/p>\n<h2 dir=\"auto\">\u4e0d\u5e38\u89c1\u7684\u539f\u59cb\u7c7b\u578b\uff08Less Common Primitives\uff09<\/h2>\n<p dir=\"auto\">\u6211\u4eec\u63d0\u4e00\u4e0b\u5728 JavaScript \u4e2d\u5269\u4f59\u7684\u4e00\u4e9b\u539f\u59cb\u7c7b\u578b\u3002\u4f46\u662f\u6211\u4eec\u5e76\u4e0d\u4f1a\u6df1\u5165\u8bb2\u89e3\u3002<\/p>\n<h3 dir=\"auto\">bigInt<\/h3>\n<p dir=\"auto\">ES2020 \u5f15\u5165\u539f\u59cb\u7c7b\u578b <code class=\"notranslate\">BigInt<\/code>\uff0c\u7528\u4e8e\u8868\u793a\u975e\u5e38\u5927\u7684\u6574\u6570\uff1a<\/p>\n<div class=\"highlight highlight-source-ts notranslate position-relative overflow-auto\" dir=\"auto\" data-snippet-clipboard-copy-content=\"\/\/ Creating a bigint via the BigInt function\nconst oneHundred: bigint = BigInt(100);\n \n\/\/ Creating a BigInt via the literal syntax\nconst anotherHundred: bigint = 100n;\"><\/p>\n<pre class=\"notranslate\"><span class=\"pl-c\">\/\/ Creating a bigint via the BigInt function<\/span>\n<span class=\"pl-k\">const<\/span> <span class=\"pl-s1\">oneHundred<\/span>: <span class=\"pl-smi\">bigint<\/span> <span class=\"pl-c1\">=<\/span> <span class=\"pl-smi\">BigInt<\/span><span class=\"pl-kos\">(<\/span><span class=\"pl-c1\">100<\/span><span class=\"pl-kos\">)<\/span><span class=\"pl-kos\">;<\/span>\n \n<span class=\"pl-c\">\/\/ Creating a BigInt via the literal syntax<\/span>\n<span class=\"pl-k\">const<\/span> <span class=\"pl-s1\">anotherHundred<\/span>: <span class=\"pl-smi\">bigint<\/span> <span class=\"pl-c1\">=<\/span> <span class=\"pl-c1\">100n<\/span><span class=\"pl-kos\">;<\/span><\/pre>\n<\/div>\n<p dir=\"auto\">\u4f60\u53ef\u4ee5\u5728 [TypeScript 3.2 \u7684\u53d1\u5e03\u65e5\u5fd7](the TypeScript 3.2 release notes)\u4e2d\u4e86\u89e3\u66f4\u591a\u4fe1\u606f\u3002<\/p>\n<h3 dir=\"auto\">symbol<\/h3>\n<p dir=\"auto\">\u8fd9\u4e5f\u662f JavaScript \u4e2d\u7684\u4e00\u4e2a\u539f\u59cb\u7c7b\u578b\uff0c\u901a\u8fc7\u51fd\u6570 <code class=\"notranslate\">Symbol()<\/code>\uff0c\u6211\u4eec\u53ef\u4ee5\u521b\u5efa\u4e00\u4e2a\u5168\u5c40\u552f\u4e00\u7684\u5f15\u7528\uff1a<\/p>\n<div class=\"highlight highlight-source-ts notranslate position-relative overflow-auto\" dir=\"auto\" data-snippet-clipboard-copy-content=\"const firstName = Symbol(&quot;name&quot;);\nconst secondName = Symbol(&quot;name&quot;);\n \nif (firstName === secondName) {\n  \/\/ This condition will always return 'false' since the types 'typeof firstName' and 'typeof secondName' have no overlap.\n  \/\/ Can't ever happen\n}\"><\/p>\n<pre class=\"notranslate\"><span class=\"pl-k\">const<\/span> <span class=\"pl-s1\">firstName<\/span> <span class=\"pl-c1\">=<\/span> <span class=\"pl-smi\">Symbol<\/span><span class=\"pl-kos\">(<\/span><span class=\"pl-s\">\"name\"<\/span><span class=\"pl-kos\">)<\/span><span class=\"pl-kos\">;<\/span>\n<span class=\"pl-k\">const<\/span> <span class=\"pl-s1\">secondName<\/span> <span class=\"pl-c1\">=<\/span> <span class=\"pl-smi\">Symbol<\/span><span class=\"pl-kos\">(<\/span><span class=\"pl-s\">\"name\"<\/span><span class=\"pl-kos\">)<\/span><span class=\"pl-kos\">;<\/span>\n \n<span class=\"pl-k\">if<\/span> <span class=\"pl-kos\">(<\/span><span class=\"pl-s1\">firstName<\/span> <span class=\"pl-c1\">===<\/span> <span class=\"pl-s1\">secondName<\/span><span class=\"pl-kos\">)<\/span> <span class=\"pl-kos\">{<\/span>\n  <span class=\"pl-c\">\/\/ This condition will always return 'false' since the types 'typeof firstName' and 'typeof secondName' have no overlap.<\/span>\n  <span class=\"pl-c\">\/\/ Can't ever happen<\/span>\n<span class=\"pl-kos\">}<\/span><\/pre>\n<\/div>\n<p dir=\"auto\">\u4f60\u53ef\u4ee5\u5728 <a href=\"https:\/\/www.typescriptlang.org\/docs\/handbook\/symbols.html\" rel=\"nofollow\">Symbol \u9875\u9762<\/a>\u4e86\u89e3\u66f4\u591a\u7684\u4fe1\u606f\u3002<\/p>\n<h2 dir=\"auto\">TypeScript \u7cfb\u5217<\/h2>\n<p dir=\"auto\">TypeScript \u7cfb\u5217\u6587\u7ae0\u7531\u5b98\u65b9\u6587\u6863\u7ffb\u8bd1\u3001\u91cd\u96be\u70b9\u89e3\u6790\u3001\u5b9e\u6218\u6280\u5de7\u4e09\u4e2a\u90e8\u5206\u7ec4\u6210\uff0c\u6db5\u76d6\u5165\u95e8\u3001\u8fdb\u9636\u3001\u5b9e\u6218\uff0c\u65e8\u5728\u4e3a\u4f60\u63d0\u4f9b\u4e00\u4e2a\u7cfb\u7edf\u5b66\u4e60 TS \u7684\u6559\u7a0b\uff0c\u5168\u7cfb\u5217\u9884\u8ba1 40 \u7bc7\u5de6\u53f3\u3002<a href=\"http:\/\/ts.yayujs.com\/\" rel=\"nofollow\">\u70b9\u6b64\u6d4f\u89c8\u5168\u7cfb\u5217\u6587\u7ae0\uff0c\u5e76\u5efa\u8bae\u987a\u4fbf\u6536\u85cf\u7ad9\u70b9\u3002<\/a><\/p>\n<p dir=\"auto\">\u5fae\u4fe1\uff1a\u300cmqyqingfeng\u300d\uff0c\u52a0\u6211\u8fdb\u51b4\u7fbd\u552f\u4e00\u7684\u8bfb\u8005\u7fa4\u3002<\/p>\n<\/td>\n<p>\u6587\u7ae0\u8f6c\u8f7d\u81ea<a href='https:\/\/github.com\/mqyqingfeng\/Blog\/issues\/229'>https:\/\/github.com\/mqyqingfeng\/Blog\/issues\/229<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"<p>TypeScript \u7684\u5b98\u65b9\u6587\u6863\u65e9\u5df2\u66f4\u65b0\uff0c\u4f46\u6211\u80fd\u627e\u5230\u7684\u4e2d\u6587\u6587\u6863\u90fd\u8fd8\u505c\u7559\u5728\u6bd4\u8f83\u8001\u7684\u7248\u672c\u3002\u6240\u4ee5\u5bf9\u5176\u4e2d\u65b0\u589e\u4ee5\u53ca\u4fee\u8ba2\u8f83\u591a\u7684\u4e00\u4e9b\u7ae0\u8282\u8fdb\u884c\u4e86\u7ffb\u8bd1\u6574\u7406\u3002 \u672c\u7bc7\u7ffb\u8bd1\u6574\u7406\u81ea Ty&#8230;<\/p>\n<p class=\"read-more\"><a class=\"btn btn-default\" 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