{"id":626,"date":"2020-02-13T15:59:49","date_gmt":"2020-02-13T07:59:49","guid":{"rendered":"http:\/\/blog.xrhoujie.com\/?p=626"},"modified":"2020-03-10T13:52:39","modified_gmt":"2020-03-10T05:52:39","slug":"typescript-%e7%ac%94%e8%ae%b0%e8%bd%ac","status":"publish","type":"post","link":"http:\/\/blog.xrhoujie.com\/?p=626","title":{"rendered":"TypeScript-\u7b14\u8bb0(\u8f6c)"},"content":{"rendered":"<div>\n<h2 class=\"heading\" data-id=\"heading-1\">ts \u7c7b\u578b<\/h2>\n<ul>\n<li>\u57fa\u672c\u7c7b\u578b\n<ul>\n<li>boolean\u3001number\u3001string\u3001symbol\u3001object\u3001null\u3001undefined<\/li>\n<li>enum<\/li>\n<li>array\u3001tuple<\/li>\n<li>any\u3001void\u3001never\u3001unknown<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<h2 class=\"heading\" data-id=\"heading-2\">\u601d\u8003\u95ee\u9898\uff1f<\/h2>\n<ul>\n<li>1\u3001Object \u548c object \u7684\u533a\u522b\uff1f<\/li>\n<li>2\u3001String \u548c string \u7684\u533a\u522b\uff1f<\/li>\n<li>3\u3001null \u548c undefined \u7684\u533a\u522b\uff1f<\/li>\n<li>3\u3001any\u3001void\u3001never\u3001unknown \u7684\u533a\u522b\uff1f<\/li>\n<\/ul>\n<h3 class=\"heading\" data-id=\"heading-3\">1.1 String \u548c string \u7684\u533a\u522b\uff1f<\/h3>\n<ul>\n<li>\u601d\u8003\u4e0b\u9762\u7684\u4ee3\u7801<\/li>\n<\/ul>\n<pre><code class=\"hljs javascript copyable\" lang=\"javascript\"><span class=\"hljs-string\">'123'<\/span> === <span class=\"hljs-keyword\">new<\/span> <span class=\"hljs-built_in\">String<\/span>(<span class=\"hljs-string\">'123'<\/span>) <span class=\"hljs-comment\">\/\/ ??<\/span>\r\n<span class=\"hljs-comment\">\/\/ false<\/span>\r\n<span class=\"hljs-keyword\">typeof<\/span> <span class=\"hljs-keyword\">new<\/span> <span class=\"hljs-built_in\">String<\/span>(<span class=\"hljs-string\">'123'<\/span>) <span class=\"hljs-comment\">\/\/ ??<\/span>\r\n<span class=\"hljs-comment\">\/\/ object<\/span>\r\n \r\n <span class=\"hljs-comment\">\/\/b \u5305\u88c5\u7c7b\u578b<\/span>\r\n<span class=\"hljs-keyword\">let<\/span> a = <span class=\"hljs-string\">'123'<\/span>, b = <span class=\"hljs-keyword\">new<\/span> <span class=\"hljs-built_in\">String<\/span>(<span class=\"hljs-string\">'123'<\/span>);\r\na.name = b.name = <span class=\"hljs-string\">'string'<\/span>;\r\n<span class=\"hljs-built_in\">console<\/span>.log(a.name, b.name); <span class=\"hljs-comment\">\/\/ ??<\/span>\r\n<span class=\"copy-code-btn\">\u590d\u5236\u4ee3\u7801<\/span><\/code><\/pre>\n<blockquote><p>\u4e0a\u9762\u7684 a.name \u4f1a\u6253\u5370 undefined,b.name \u53ef\u4ee5\u6b63\u5e38\u7684\u6253\u5370\u51fa &#8216;string&#8217;<\/p><\/blockquote>\n<h3 class=\"heading\" data-id=\"heading-4\">\u533a\u5206\u539f\u59cb\u7c7b\u578b\u548c\u5305\u88c5\u7c7b\u578b\uff08wrapper object\uff09<\/h3>\n<ul>\n<li>\u800cTS\u4e2d\u7684string\u3001boolean\u3001number\u7b49\u58f0\u660e\u7c7b\u578b\uff0c\u5219\u662f\u6307\u539f\u59cb\u7684\u57fa\u672c\u6570\u636e\u7c7b\u578b\u3002<\/li>\n<\/ul>\n<pre><code class=\"hljs javascript copyable\" lang=\"javascript\"><span class=\"hljs-keyword\">let<\/span> str: string = <span class=\"hljs-keyword\">new<\/span> <span class=\"hljs-built_in\">String<\/span>(<span class=\"hljs-number\">123<\/span>); <span class=\"hljs-comment\">\/\/ error: Type 'String' is not assignable to type 'string'.<\/span>\r\n<span class=\"hljs-keyword\">let<\/span> str: string = <span class=\"hljs-string\">'123'<\/span>; <span class=\"hljs-comment\">\/\/ ok<\/span>\r\n<span class=\"hljs-keyword\">let<\/span> str: <span class=\"hljs-built_in\">String<\/span> = <span class=\"hljs-string\">'123'<\/span>; <span class=\"hljs-comment\">\/\/ ok<\/span>\r\n \r\n<span class=\"hljs-keyword\">let<\/span> a = <span class=\"hljs-keyword\">new<\/span> <span class=\"hljs-built_in\">String<\/span>(<span class=\"hljs-number\">1234<\/span>);\r\n<span class=\"hljs-keyword\">let<\/span>: str: <span class=\"hljs-keyword\">typeof<\/span> <span class=\"hljs-string\">'1234'<\/span>; <span class=\"hljs-comment\">\/\/ str: string<\/span>\r\n<span class=\"hljs-keyword\">let<\/span> str: <span class=\"hljs-keyword\">typeof<\/span> a; <span class=\"hljs-comment\">\/\/str: String<\/span>\r\n<span class=\"copy-code-btn\">\u590d\u5236\u4ee3\u7801<\/span><\/code><\/pre>\n<h3 class=\"heading\" data-id=\"heading-5\">2.1 Object \u548c object \u7684\u533a\u522b\uff1f<\/h3>\n<ul>\n<li>\u5728js\u4e2d\uff0cBoolean\u3001String\u3001Number\u4e3a\u57fa\u672c\u5305\u88c5\u7c7b\u578b\u7684\u6784\u9020\u51fd\u6570\uff08\u7c7b\uff09\u3002\u5728TS\u4e2d\uff0c\u4ed6\u4eec\u5728\u7c7b\u578b\u58f0\u660e\u4e0a\u4e0b\u6587\u4e2d\uff0c\u5219\u6307\u4ee3\u63a5\u53e3\u5b9a\u4e49\uff1a<\/li>\n<\/ul>\n<pre><code class=\"hljs javascript copyable\" lang=\"javascript\">interface <span class=\"hljs-built_in\">String<\/span> {\r\n    <span class=\"hljs-comment\">\/** Returns a string representation of a string. *\/<\/span>\r\n    toString(): string;\r\n \r\n    <span class=\"hljs-comment\">\/**\r\n      * Returns the character at the specified index.\r\n      * @param pos The zero-based index of the desired character.\r\n      *\/<\/span>\r\n    charAt(pos: number): string;\r\n \r\n    <span class=\"hljs-comment\">\/**\r\n      * Returns the Unicode value of the character at the specified location.\r\n      * @param index The zero-based index of the desired character. If there is no character at the specified index, NaN is returned.\r\n      *\/<\/span>\r\n    charCodeAt(index: number): number;\r\n \r\n \r\n    ...\r\n}\r\n\r\n<span class=\"copy-code-btn\">\u590d\u5236\u4ee3\u7801<\/span><\/code><\/pre>\n<blockquote><p>\u5373\uff0c\u5728TS\u4e2d\uff0cnew String(&#8230;) \u8fd9\u91cc\u7684String\u662f\u6307\u5bf9\u4e8einterface String\u7684\u7c7b\u5b9e\u73b0\uff08class implements\uff09\u3002<\/p><\/blockquote>\n<ul>\n<li>\u800c\u5728\u7c7b\u578b\u58f0\u660e\u4e0a\u4e0b\u6587\u4e2d\uff0cString\u5219\u6307\u7684\u5c31\u662f\u8fd9\u4e2ainterface String\u3002<\/li>\n<li>2.1.1 Object \u5176\u5b9e\u4e5f\u662f\u4e00\u4e2a\u63a5\u53e3\u58f0\u660e\uff0c\u53ef\u4ee5\u53bb\u770b\u770b ts \u6e90\u4ee3\u7801\u7684 Object \u662f\u600e\u4e48\u58f0\u660e\u7684\u3002\u4efb\u610f\u7c7b\u578b\u90fd\u662f Object<\/li>\n<\/ul>\n<pre><code class=\"hljs javascript copyable\" lang=\"javascript\"><span class=\"hljs-keyword\">let<\/span> num: <span class=\"hljs-built_in\">Object<\/span> = <span class=\"hljs-number\">1<\/span>; <span class=\"hljs-comment\">\/\/ ok<\/span>\r\n<span class=\"hljs-keyword\">let<\/span> str: <span class=\"hljs-built_in\">Object<\/span> = <span class=\"hljs-string\">'a'<\/span>; <span class=\"hljs-comment\">\/\/ ok<\/span>\r\n<span class=\"hljs-keyword\">let<\/span> obj: <span class=\"hljs-built_in\">Object<\/span> = { <span class=\"hljs-attr\">foo<\/span>: <span class=\"hljs-number\">123<\/span> }; <span class=\"hljs-comment\">\/\/ ok<\/span>\r\n<span class=\"hljs-keyword\">let<\/span> nul: <span class=\"hljs-built_in\">Object<\/span> = <span class=\"hljs-literal\">null<\/span>; <span class=\"hljs-comment\">\/\/ error<\/span>\r\n<span class=\"hljs-keyword\">let<\/span> undef: <span class=\"hljs-built_in\">Object<\/span> = <span class=\"hljs-literal\">undefined<\/span>; <span class=\"hljs-comment\">\/\/ error<\/span>\r\n \r\n \r\nobj.foo <span class=\"hljs-comment\">\/\/ error: Property 'foo' does not exist on type '{}'<\/span>\r\nobj.toString() <span class=\"hljs-comment\">\/\/ ok<\/span>\r\n<span class=\"copy-code-btn\">\u590d\u5236\u4ee3\u7801<\/span><\/code><\/pre>\n<blockquote><p>\u4e8b\u5b9e\u4e0a\uff0c\u58f0\u660e\u4e3aObject\u53ef\u4ee5\u8d4b\u4e88\u9664\u4e86null\u3001undefined\u4ee5\u5916\u7684\u4efb\u610f\u503c\uff01\u6b64\u65f6\u8bbf\u95ee\u8fd9\u4e9b\u58f0\u660e\u7684\u53d8\u91cf\uff0c\u90fd\u53ef\u4ee5\u8bbf\u95eeObject\u63a5\u53e3\u6240\u5b9a\u4e49\u7684\u51e0\u4e2a\u57fa\u672c\u65b9\u6cd5\u3002<\/p><\/blockquote>\n<ul>\n<li>2.1.2 {}:\u800c\u7a7a\u7684\u82b1\u62ec\u53f7{}\u7c7b\u578b\uff0c\u5219\u548cObject\u5f88\u7c7b\u4f3c\uff0c\u540c\u6837\u53ef\u4ee5\u63a5\u53d7\u4efb\u610f\u7c7b\u578b\u7684\u503c\u3002\u5b83\u662f\u6307\u7a7a\u5bf9\u8c61\u7c7b\u578b\u3002\u58f0\u660e\u4e3a{}\u7c7b\u578b\uff0c\u5219\u6ca1\u6709\u4efb\u4f55\u6210\u5458\u53d8\u91cf\u53ef\u4ee5\u8bbf\u95ee\uff08\u8fdeObject.prototype.toString\u7b49\u65b9\u6cd5\u90fd\u4e0d\u53ef\u4ee5\uff09<\/li>\n<\/ul>\n<pre><code class=\"hljs javascript copyable\" lang=\"javascript\"><span class=\"hljs-keyword\">let<\/span> num: {} = <span class=\"hljs-number\">1<\/span>; <span class=\"hljs-comment\">\/\/ ok<\/span>\r\n<span class=\"hljs-keyword\">let<\/span> str: {} = <span class=\"hljs-string\">'a'<\/span>; <span class=\"hljs-comment\">\/\/ ok<\/span>\r\n<span class=\"hljs-keyword\">let<\/span> obj: {} = { <span class=\"hljs-attr\">foo<\/span>: <span class=\"hljs-number\">1234<\/span> }; <span class=\"hljs-comment\">\/\/ ok<\/span>\r\n<span class=\"hljs-keyword\">let<\/span> nul: {} = <span class=\"hljs-literal\">null<\/span>; <span class=\"hljs-comment\">\/\/ error<\/span>\r\n<span class=\"hljs-keyword\">let<\/span> undef: {} = <span class=\"hljs-literal\">undefined<\/span>; <span class=\"hljs-comment\">\/\/ error<\/span>\r\n \r\n \r\nobj.foo <span class=\"hljs-comment\">\/\/ error: Property 'foo' does not exist on type '{}'<\/span>\r\nobj.toString() <span class=\"hljs-comment\">\/\/ error: Property 'toString' does not exist on type '{}'<\/span>\r\n\r\n<span class=\"copy-code-btn\">\u590d\u5236\u4ee3\u7801<\/span><\/code><\/pre>\n<ul>\n<li>2.1.3 object : object\u7c7b\u578b\uff0c\u5219\u5355\u7eaf\u6307\u4ee3\u975estring\u3001number\u3001boolean\u3001symbol\u3001null\u3001undefined\u7684\u5176\u4ed6\u7c7b\u578b\uff01\u4e0e{}\u7c7b\u4f3c\uff0c\u540c\u6837\u6ca1\u6709\u4efb\u4f55\u6210\u5458\u5c5e\u6027\u6216\u65b9\u6cd5\u53ef\u4ee5\u8bbf\u95ee\uff01<\/li>\n<\/ul>\n<pre><code class=\"hljs javascript copyable\" lang=\"javascript\"><span class=\"hljs-comment\">\/\/ \u8fd9\u4e48\u8d4b\u503c<\/span>\r\n<span class=\"hljs-keyword\">let<\/span> num: object = <span class=\"hljs-number\">1<\/span>; <span class=\"hljs-comment\">\/\/ error<\/span>\r\n<span class=\"hljs-keyword\">let<\/span> str: object = <span class=\"hljs-string\">'a'<\/span>; <span class=\"hljs-comment\">\/\/ error<\/span>\r\n<span class=\"hljs-keyword\">let<\/span> obj: object = { <span class=\"hljs-attr\">foo<\/span>: <span class=\"hljs-number\">1234<\/span> }; <span class=\"hljs-comment\">\/\/ ok<\/span>\r\n<span class=\"hljs-keyword\">let<\/span> nul: object = <span class=\"hljs-literal\">null<\/span>; <span class=\"hljs-comment\">\/\/ error<\/span>\r\n<span class=\"hljs-keyword\">let<\/span> undef: object = <span class=\"hljs-literal\">undefined<\/span>; <span class=\"hljs-comment\">\/\/ error<\/span>\r\n \r\n \r\nobj.foo <span class=\"hljs-comment\">\/\/ error: Property 'foo' does not exist on type 'object'<\/span>\r\nobj.toString() <span class=\"hljs-comment\">\/\/ error: Property 'toString' does not exist on type 'object'<\/span>\r\n\r\n<span class=\"copy-code-btn\">\u590d\u5236\u4ee3\u7801<\/span><\/code><\/pre>\n<ul>\n<li>\u7c7b\u578b\u7684\u68c0\u6d4b\u7684\u5bbd\u6cdb\u5ea6\uff1a<strong>\u7c7b\u578b\u9650\u5236\u8303\u56f4\u4e0a\uff1aany &gt; {} ~ Object &gt; object<\/strong><\/li>\n<\/ul>\n<blockquote><p>\u603b\u7ed3: \u8868\u793a\u57fa\u672c\u5bf9\u8c61\u7c7b\u578b\u65f6\uff0c\u5e94\u5f53\u603b\u662f\u4f7f\u7528object\u7c7b\u578b\uff0c\u6216\u8005\u4f7f\u7528\u63a5\u53e3\u5b9a\u4e49\u7ed3\u6784\u5316\u5bf9\u8c61\u3002<\/p><\/blockquote>\n<h3 class=\"heading\" data-id=\"heading-6\">3.1 null \u548c undefined \u7684\u533a\u522b\uff1f<\/h3>\n<ul>\n<li>ts\u4e2d\u4e5f\u6709null\u548cundefined\u7c7b\u578b\uff0c\u58f0\u660e\u4e3a\u8fd9\u4e24\u79cd\u7c7b\u578b\u7684\u503c\uff0c\u4e5f\u53ea\u80fd\u8d4b\u4e88\u540c\u540d\u503c\uff1a<\/li>\n<\/ul>\n<pre><code class=\"hljs bash copyable\" lang=\"bash\"><span class=\"hljs-built_in\">let<\/span> a: null = null;\r\n<span class=\"hljs-built_in\">let<\/span> b: undefined = undefined;\r\n<span class=\"copy-code-btn\">\u590d\u5236\u4ee3\u7801<\/span><\/code><\/pre>\n<ul>\n<li>\u5728\u9ed8\u8ba4\u60c5\u51b5\u4e0b\uff0cnull\u548cundefined\u8fd9\u4e24\u4e2a\u503c\uff08\u4e0d\u662f\u6307\u7c7b\u578b\uff01\uff01\uff09\u88ab\u5f53\u4f5c\u5176\u4ed6\u7c7b\u578b\u7684\u5b50\u7c7b\u578b\uff0c\u5373\u53ef\u4ee5\u8d4b\u4e88\u4efb\u610f\u5176\u4ed6\u7c7b\u578b\u58f0\u660e\u7684\u53d8\u91cf\u3002\u4f46\u662f\u5728\u5f00\u542f\u4e86 &#8211;strictNullChecks \u7f16\u8bd1\u9009\u9879\u540e\uff0c\u4ed6\u4eec\u5219\u53ea\u80fd\u88ab\u8d4b\u4e88void\u7c7b\u578b\uff0c\u6216\u8005\u5404\u81ea\u7684\u540c\u540d\u7c7b\u578b\u3002<\/li>\n<\/ul>\n<pre><code class=\"hljs bash copyable\" lang=\"bash\"><span class=\"hljs-built_in\">let<\/span> a: void = null;\r\n<span class=\"hljs-built_in\">let<\/span> b: void = undefined;\r\n<span class=\"copy-code-btn\">\u590d\u5236\u4ee3\u7801<\/span><\/code><\/pre>\n<h3 class=\"heading\" data-id=\"heading-7\">4.1 any\u3001void\u3001never\u3001unknown \u7684\u533a\u522b<\/h3>\n<ul>\n<li>4.1.1 any ts \u68c0\u6d4b\u5f31\uff0c\u517c\u5bb9\u6027\u95ee\u9898\u89e3\u51b3\u65b9\u6848\u3002<\/li>\n<li>\u6210\u5458\u8bbf\u95ee\u65e0\u9650\u5236<\/li>\n<\/ul>\n<pre><code class=\"hljs bash copyable\" lang=\"bash\"><span class=\"hljs-built_in\">let<\/span> user: any = {};\r\n \r\nuser.name \/\/ ok\r\n<span class=\"copy-code-btn\">\u590d\u5236\u4ee3\u7801<\/span><\/code><\/pre>\n<blockquote><p>\u5982\u4ee5\u4e0a\u4f8b\u5b50\u4e2d\uff0cuser\u88ab\u58f0\u660e\u4e3aany\u7c7b\u578b\uff0c\u5373\u4f7f\u5176\u6ca1\u6709name\u8fd9\u4e2a\u5c5e\u6027\uff0ctsc\u4e5f\u4e0d\u4f1a\u5bf9\u5176\u8fdb\u884c\u68c0\u67e5\u3002\u6240\u4ee5any\u53ef\u4ee5\u7528\u6765\u6307\u4ee3\u54ea\u4e9b\u7531\u5916\u90e8\u4f20\u5165\u3001\u670d\u52a1\u7aef\u8fd4\u56de\u7b49\u9ed1\u76d2\u5b50\u7ed3\u6784\u7684\u6570\u636e\uff01\uff01<\/p><\/blockquote>\n<ul>\n<li>\u4e8b\u5b9e\u4e0a\uff0c\u4efb\u610f\u672a\u660e\u786e\u58f0\u660e\u7c7b\u578b\u5e76\u5207\u65e0\u6cd5\u63a8\u5bfc\u51fa\u7c7b\u578b\u7684\u503c\u90fd\u9ed8\u8ba4\u4e3aany\u7c7b\u578b\u3002<\/li>\n<\/ul>\n<pre><code class=\"hljs bash copyable\" lang=\"bash\"><span class=\"hljs-built_in\">let<\/span> a; \/\/ a: any\r\na = 1;\r\n<span class=\"hljs-built_in\">let<\/span> a = 1; \/\/a: number\r\n<span class=\"copy-code-btn\">\u590d\u5236\u4ee3\u7801<\/span><\/code><\/pre>\n<ul>\n<li>4.1.2 void<\/li>\n<\/ul>\n<p>void\u5e94\u5f53\u4ec5\u4ec5\u7528\u4e8e\u51fd\u6570\u58f0\u660e\uff0c\u5373\u6ca1\u6709\u660e\u786e\u8fd4\u56de\u503c\u7684\u51fd\u6570\uff0c\u5e94\u8be5\u88ab\u58f0\u660e\u4e3avoid\u7c7b\u578b\u3002\u5c06void\u7528\u6237\u53d8\u91cf\u58f0\u660e\uff0c\u5219\u53ea\u80fd\u4e3a\u5176\u8d4b\u4e88null\u6216undefined\u3002<\/p>\n<ul>\n<li>4.1.3 never<\/li>\n<\/ul>\n<p>never\u7528\u4e8e\u51fd\u6570\u8fd4\u56de\u503c\u65f6\uff0c\u8868\u793a\u51fd\u6570\u6709\u629b\u51fa\u5f02\u5e38\uff0c\u6ca1\u6709\u6b63\u5e38\u6267\u884c\u5230\u5e95\u3002\u7528\u4e8e\u53d8\u91cf\u58f0\u660e\uff0c\u65e0\u6cd5\u4e3a\u5176\u8d4b\u4e88\u4efb\u4f55\u503c\uff01<\/p>\n<p>never\u662f\u6240\u6709\u7c7b\u578b\u7684\u5b50\u7c7b\u578b\u5e76\u4e14\u53ef\u4ee5\u8d4b\u503c\u7ed9\u6240\u6709\u7c7b\u578b\u3002 \u6ca1\u6709\u7c7b\u578b\u662fnever\u7684\u5b50\u7c7b\u578b\u6216\u80fd\u8d4b\u503c\u7ed9never\uff08never\u7c7b\u578b\u672c\u8eab\u9664\u5916\uff09\u3002<\/p>\n<p>\u5728\u51fd\u6570\u8868\u8fbe\u5f0f\u6216\u7bad\u5934\u51fd\u6570\u6ca1\u6709\u8fd4\u56de\u7c7b\u578b\u6ce8\u89e3\u65f6\uff0c\u5982\u679c\u51fd\u6570\u6ca1\u6709return\u8bed\u53e5\uff0c\u6216\u8005\u53ea\u6709never\u7c7b\u578b\u8868\u8fbe\u5f0f\u7684return\u8bed\u53e5\uff0c\u5e76\u4e14\u5982\u679c\u51fd\u6570\u662f\u4e0d\u53ef\u6267\u884c\u5230\u7ec8\u70b9\u7684\uff08\u4f8b\u5982\u901a\u8fc7\u63a7\u5236\u6d41\u5206\u6790\u51b3\u5b9a\u7684\uff09\uff0c\u5219\u63a8\u65ad\u51fd\u6570\u7684\u8fd4\u56de\u7c7b\u578b\u662fnever\u3002<\/p>\n<p>\u5728\u6709\u660e\u786enever\u8fd4\u56de\u7c7b\u578b\u6ce8\u89e3\u7684\u51fd\u6570\u4e2d\uff0c\u6240\u6709return\u8bed\u53e5\uff08\u5982\u679c\u6709\u7684\u8bdd\uff09\u5fc5\u987b\u6709never\u7c7b\u578b\u7684\u8868\u8fbe\u5f0f\u5e76\u4e14\u51fd\u6570\u7684\u7ec8\u70b9\u5fc5\u987b\u662f\u4e0d\u53ef\u6267\u884c\u7684\u3002<\/p>\n<ul>\n<li>never\u8fd8\u53ef\u4ee5\u7528\u4e8e\u6620\u5c04\u7c7b\u578b\u4e2d\u8868\u8fbe\u5f0f\uff0c\u7528\u4e8e\u5220\u9664\/\u8fc7\u6ee4\u5f53\u524d\u7c7b\u578b<\/li>\n<\/ul>\n<pre><code class=\"hljs bash copyable\" lang=\"bash\"><span class=\"hljs-built_in\">let<\/span> a: string | never; \/\/ a: string\r\n<span class=\"hljs-built_in\">type<\/span> Exclude&lt;T, K&gt; = T extends K ? never: T;\r\n<span class=\"copy-code-btn\">\u590d\u5236\u4ee3\u7801<\/span><\/code><\/pre>\n<ul>\n<li>4.1.4 unknown<\/li>\n<\/ul>\n<blockquote><p>unknown\u76f8\u5bf9\u4e8eany\uff0c\u4efb\u610f\u7c7b\u578b\u90fd\u53ef\u4ee5\u8d4b\u503c\u7ed9unknow\uff0c\u4f46\u662f\u4e0d\u53ef\u5bf9\u5176\u8fdb\u884c\u4efb\u4f55\u8bbf\u95ee\u64cd\u4f5c\uff08\u4ec5\u4ec5\u4e3a\u7c7b\u578b\u5b89\u5168\uff0cany\u64cd\u4f5c\u8bbf\u95ee\u4e5f\u5b89\u5168\uff09<\/p><\/blockquote>\n<pre><code class=\"hljs bash copyable\" lang=\"bash\"><span class=\"hljs-built_in\">let<\/span> a: any = 123;\r\na.toFixed(); \/\/ok\r\n<span class=\"hljs-built_in\">let<\/span> a: unknown = 123;\r\na.toFixed(); \/\/ error\r\n<span class=\"copy-code-btn\">\u590d\u5236\u4ee3\u7801<\/span><\/code><\/pre>\n<h2 class=\"heading\" data-id=\"heading-8\">\u672a\u5b8c\u5f85\u7eed&#8230;<\/h2>\n<\/div>\n<p>\u4f5c\u8005\uff1aPandaaa<br \/>\n\u94fe\u63a5\uff1ahttps:\/\/juejin.im\/post\/5be41db55188257c3079bfa1<\/p>\n","protected":false},"excerpt":{"rendered":"<p>ts \u7c7b\u578b \u57fa\u672c\u7c7b\u578b boolean\u3001number\u3001string\u3001symbol\u3001object\u3001null\u3001und [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":145,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[8],"tags":[23],"_links":{"self":[{"href":"http:\/\/blog.xrhoujie.com\/index.php?rest_route=\/wp\/v2\/posts\/626"}],"collection":[{"href":"http:\/\/blog.xrhoujie.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/blog.xrhoujie.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/blog.xrhoujie.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/blog.xrhoujie.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=626"}],"version-history":[{"count":1,"href":"http:\/\/blog.xrhoujie.com\/index.php?rest_route=\/wp\/v2\/posts\/626\/revisions"}],"predecessor-version":[{"id":627,"href":"http:\/\/blog.xrhoujie.com\/index.php?rest_route=\/wp\/v2\/posts\/626\/revisions\/627"}],"wp:featuredmedia":[{"embeddable":true,"href":"http:\/\/blog.xrhoujie.com\/index.php?rest_route=\/wp\/v2\/media\/145"}],"wp:attachment":[{"href":"http:\/\/blog.xrhoujie.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=626"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/blog.xrhoujie.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=626"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/blog.xrhoujie.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=626"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}