1"use strict";(self.webpackChunkcode_fictionist=self.webpackChunkcode_fictionist||[]).push([[3695],{28453:(e,n,c)=>{c.d(n,{R:()=>d,x:()=>o});var s=c(96540);const r={},i=s.createContext(r);function d(e){const n=s.useContext(i);return s.useMemo((function(){return"function"==typeof e?e(n):{...n,...e}}),[n,e])}function o(e){let n;return n=e.disableParentContext?"function"==typeof e.components?e.components(r):e.components||r:d(e.components),s.createElement(i.Provider,{value:n},e.children)}},74631:(e,n,c)=>{c.r(n),c.d(n,{assets:()=>l,contentTitle:()=>o,default:()=>j,frontMatter:()=>d,metadata:()=>s,toc:()=>a});const s=JSON.parse('{"id":"series/iThome_2025/day_04","title":"Day04 - \u5927\u5bb6\u90fd\u5728\u8aaa\u7684\u8b8a\u6578\u4f5c\u7528\u57df\u548c\u63d0\u5347\u5230\u5e95\u8aaa\u4e86\u4ec0\u9ebc\u6545\u4e8b\uff1f","description":"\u95dc\u65bc Javascript \u7684\u8b8a\u6578\u5ba3\u544a\u8207\u8b8a\u6578\u4f5c\u7528\u57df\u5176\u5be6\u4e5f\u662f\u500b\u8001\u751f\u5e38\u8ac7\u7684\u554f\u984c\u3002\u57fa\u672c\u4e0a\u9762\u8a66\u88e1\u7e3d\u662f\u559c\u6b61\u585e\u500b\u5e7e\u984c\u8003\u8003\u8b8a\u6578\u7684\u6982\u5ff5\u3002","source":"@site/docs/series/02-iThome_2025/04-day_04.mdx","sourceDirName":"series/02-iThome_2025","slug":"/series/iThome_2025/day_04","permalink":"/docs/series/iThome_2025/day_04","draft":false,"unlisted":false,"tags":[{"inline":true,"label":"JavaScript","permalink":"/docs/tags/java-script"},{"inline":true,"label":"variable","permalink":"/docs/tags/variable"},{"inline":true,"label":"scope","permalink":"/docs/tags/scope"},{"inline":true,"label":"hoisting","permalink":"/docs/tags/hoisting"}],"version":"current","lastUpdatedAt":1766374113000,"sidebarPosition":4,"frontMatter":{"title":"Day04 - \u5927\u5bb6\u90fd\u5728\u8aaa\u7684\u8b8a\u6578\u4f5c\u7528\u57df\u548c\u63d0\u5347\u5230\u5e95\u8aaa\u4e86\u4ec0\u9ebc\u6545\u4e8b\uff1f","sidebar_label":"Day04 - \u5927\u5bb6\u90fd\u5728\u8aaa\u7684\u8b8a\u6578\u4f5c\u7528\u57df\u548c\u63d0\u5347\u5230\u5e95\u8aaa\u4e86\u4ec0\u9ebc\u6545\u4e8b\uff1f","tags":["JavaScript","variable","scope","hoisting"],"keywords":["JavaScript","variable","scope","hoisting"]},"sidebar":"series","previous":{"title":"Day03 - CSS \u7684\u300c\u76f8\u5c0d\u300d\u6982\u5ff5","permalink":"/docs/series/iThome_2025/day_03"},"next":{"title":"Day05 - \u54bb\uff01\u98db\u904e\u53bb\u7684\u662f arrow function \u9084\u662f function\uff1f","permalink":"/docs/series/iThome_2025/day_05"}}');var r=c(74848),i=c(28453);const d={title:"Day04 - \u5927\u5bb6\u90fd\u5728\u8aaa\u7684\u8b8a\u6578\u4f5c\u7528\u57df\u548c\u63d0\u5347\u5230\u5e95\u8aaa\u4e86\u4ec0\u9ebc\u6545\u4e8b\uff1f",sidebar_label:"Day04 - \u5927\u5bb6\u90fd\u5728\u8aaa\u7684\u8b8a\u6578\u4f5c\u7528\u57df\u548c\u63d0\u5347\u5230\u5e95\u8aaa\u4e86\u4ec0\u9ebc\u6545\u4e8b\uff1f",tags:["JavaScript","variable","scope","hoisting"],keywords:["JavaScript","variable","scope","hoisting"]},o=void 0,l={},a=[{value:"\u95dc\u65bc <code>var</code>\u3001<code>let</code>\u3001<code>const</code> \u7684\u611b\u6068\u60c5\u4ec7",id:"\u95dc\u65bc-varletconst-\u7684\u611b\u6068\u60c5\u4ec7",level:2},{value:"\u51fd\u5f0f\u4f5c\u7528\u57df vs \u5340\u584a\u4f5c\u7528\u57df",id:"\u51fd\u5f0f\u4f5c\u7528\u57df-vs-\u5340\u584a\u4f5c\u7528\u57df",level:3},{value:"\u63d0\u5347 (Hoisting)",id:"\u63d0\u5347-hoisting",level:2}];function t(e){const n={admonition:"admonition",blockquote:"blockquote",br:"br",code:"code",h2:"h2",h3:"h3",li:"li",ol:"ol",p:"p",pre:"pre",ul:"ul",...(0,i.R)(),...e.components};return(0,r.jsxs)(r.Fragment,{children:[(0,r.jsxs)(n.p,{children:["\u95dc\u65bc Javascript \u7684\u8b8a\u6578\u5ba3\u544a\u8207\u8b8a\u6578\u4f5c\u7528\u57df\u5176\u5be6\u4e5f\u662f\u500b\u8001\u751f\u5e38\u8ac7\u7684\u554f\u984c\u3002\u57fa\u672c\u4e0a\u9762\u8a66\u88e1\u7e3d\u662f\u559c\u6b61\u585e\u500b\u5e7e\u984c\u8003\u8003\u8b8a\u6578\u7684\u6982\u5ff5\u3002",(0,r.jsx)(n.br,{}),"\n","\u5361\u65af\u4f2f\u9019\u4f4d\u696d\u754c\u524d\u8f29\u6709\u4e00\u672c\u633a\u6709\u540d\u7684\u8457\u4f5c\u300a\u5e36\u4f60\u7121\u75db\u63d0\u5347 JavaScript \u9762\u8a66\u529b\u300b\uff0c\u88e1\u9762\u7b2c\u4e00\u7ae0\u5c31\u82b1\u4e86\u6574\u500b\u7ae0\u7bc0\u5728\u8b1b\u9019\u4ef6\u4e8b\uff0c\u53ef\u898b\u8b8a\u6578\u7684\u6982\u5ff5\u6709\u591a\u91cd\u8981\u3002",(0,r.jsx)(n.br,{}),"\n","(\u662f\u8aaa\uff0c\u4e0d\u662f\u696d\u914d\uff0c\u4f46\u9019\u672c\u66f8\u771f\u7684\u5beb\u7684\u4e0d\u932f)"]}),"\n",(0,r.jsxs)(n.h2,{id:"\u95dc\u65bc-varletconst-\u7684\u611b\u6068\u60c5\u4ec7",children:["\u95dc\u65bc ",(0,r.jsx)(n.code,{children:"var"}),"\u3001",(0,r.jsx)(n.code,{children:"let"}),"\u3001",(0,r.jsx)(n.code,{children:"const"})," \u7684\u611b\u6068\u60c5\u4ec7"]}),"\n",(0,r.jsxs)(n.p,{children:["\u9019\u5e7e\u5e74\u65b0\u5b78 JavaScript \u7684\uff0c\u61c9\u8a72\u90fd\u6703\u88ab\u547c\u7c72\u4f7f\u7528 ",(0,r.jsx)(n.code,{children:"let"})," \u548c ",(0,r.jsx)(n.code,{children:"const"})," \u4f86\u53d6\u4ee3 ",(0,r.jsx)(n.code,{children:"var"}),"\u3002",(0,r.jsx)(n.br,{}),"\n","\u7406\u7531\u6211\u807d\u904e\u6700\u591a\u4eba\u8aaa\u7684\u662f\uff1a"]}),"\n",(0,r.jsxs)(n.blockquote,{children:["\n",(0,r.jsxs)(n.p,{children:[(0,r.jsx)(n.code,{children:"var"})," \u5f88\u5371\u96aa\u554a\uff01\u6703\u5ba3\u544a\u6210\u300c\u5168\u57df\u8b8a\u6578\u300d\uff0c\u5bb9\u6613\u6703\u
16709\u8b8a\u6578\u6c59\u67d3\u554a\uff01"]}),"\n"]}),"\n",(0,r.jsxs)(n.p,{children:["Well\uff0c\u4e0d\u80fd\u8aaa\u9019\u662f\u932f\u7684\uff0c\u9019\u53e5\u8a71\u5176\u5be6\u4e5f\u662f\u6982\u62ec\u63cf\u8ff0\u4e86\u7528 ",(0,r.jsx)(n.code,{children:"var"})," \u7684\u5371\u96aa\u6027\u3002",(0,r.jsx)(n.br,{}),"\n","\u4f46\u5b83\u662f\u4e0d\u7cbe\u78ba\u7684\uff0c\u90e8\u5206\u4eba\u6703\u56e0\u70ba\u9019\u53e5\u8a71\u8aa4\u6703\u7528 ",(0,r.jsx)(n.code,{children:"var"})," \u5ba3\u544a\u7684\u8b8a\u6578\u5c31\u4e00\u5b9a\u662f\u5168\u57df\u8b8a\u6578\uff0c\u9019\u5c0d\u65bc\u4f5c\u7528\u57df\u7684\u7406\u89e3\u662f\u76f8\u7576\u81f4\u547d\u7684\u3002",(0,r.jsx)(n.br,{}),"\n","\u6240\u4ee5\u5176\u5be6\u9019\u53e5\u8a71\u7406\u61c9\u66f4\u6b63\u6210\uff1a"]}),"\n",(0,r.jsxs)(n.blockquote,{children:["\n",(0,r.jsxs)(n.p,{children:[(0,r.jsx)(n.code,{children:"var"})," \u5f88\u5371\u96aa\u554a\uff01\u4ed6\u6709\u300c\u6a5f\u6703\u300d\u5ba3\u544a\u6210\u300c\u5168\u57df\u8b8a\u6578\u300d\uff0c\u5bb9\u6613\u6703\u6709\u8b8a\u6578\u6c59\u67d3\u554a\uff01"]}),"\n"]}),"\n",(0,r.jsxs)(n.p,{children:["\u55ef\uff0c\u6a5f\u6703\uff0c\u8868\u793a\u662f\u4e00\u7a2e\u6f5b\u5728\u7684\u98a8\u96aa\u3002",(0,r.jsx)(n.br,{}),"\n","\u800c ",(0,r.jsx)(n.code,{children:"let"})," \u548c ",(0,r.jsx)(n.code,{children:"const"})," \u6703\u88ab\u63a8\u5d07\uff0c\u5c31\u662f\u56e0\u70ba\u4ed6\u5011\u964d\u4f4e\u4e86\u9019\u500b\u6f5b\u5728\u98a8\u96aa\u767c\u751f\u7684\u53ef\u80fd\u3002"]}),"\n",(0,r.jsx)(n.h3,{id:"\u51fd\u5f0f\u4f5c\u7528\u57df-vs-\u5340\u584a\u4f5c\u7528\u57df",children:"\u51fd\u5f0f\u4f5c\u7528\u57df vs \u5340\u584a\u4f5c\u7528\u57df"}),"\n",(0,r.jsxs)(n.p,{children:["\u6240\u4ee5\u4f86\u8ac7\u8ac7 ",(0,r.jsx)(n.code,{children:"var"})," \u662f\u5982\u4f55\u6f5b\u5728\u9020\u6210\u5ba3\u544a\u5168\u57df\u8b8a\u6578\u98a8\u96aa\uff0c\u4ee5\u53ca ",(0,r.jsx)(n.code,{children:"let"})," \u548c ",(0,r.jsx)(n.code,{children:"const"})," \u53c8\u662f\u5982\u4f55\u964d\u4f4e\u9019\u500b\u98a8\u96aa\u7684\u3002",(0,r.jsx)(n.br,{}),"\n","\u9019\u5c31\u5f97\u5f9e\u4ed6\u5011\u7684\u4f5c\u7528\u57df\u958b\u59cb\u8aaa\u8d77\u3002"]}),"\n",(0,r.jsxs)(n.p,{children:["\u6211\u76f8\u4fe1\u5927\u90e8\u5206\u4eba\u90fd\u80fd\u56de\u7b54\u51fa ",(0,r.jsx)(n.code,{children:"var"})," \u662f\u300c\u51fd\u5f0f\u4f5c\u7528\u57df\u300d\uff0c\u90a3\u6211\u5c31\u60f3\u554f\uff0c\u6709\u4f5c\u7528\u57df\u5c31\u8868\u793a\u6709\u4ed6\u4f5c\u7528\u7684\u7bc4\u570d\uff0c\u90a3\u70ba\u4f55\u5927\u5bb6\u5e38\u6703\u8aaa ",(0,r.jsx)(n.code,{children:"var"})," \u6703\u5ba3\u544a\u6210\u5168\u57df\u8b8a\u6578\uff1f",(0,r.jsx)(n.br,{}),"\n","\u5176\u5be6\u7c21\u55ae\u4f86\u770b\u4e0b\u9762\u4f8b\u5b50\uff1a"]}),"\n",(0,r.jsx)(n.pre,{children:(0,r.jsx)(n.code,{className:"language-javascript",children:"function test () {\n var name = 'Jeremy'\n console.log(name)\n}\n\ntest() // Jeremy\nconsole.log(name) // ReferenceError: name is not defined\n"})}),"\n",(0,r.jsxs)(n.p,{children:["\u9019\u500b\u7c21\u55ae\u7684\u7bc4\u4f8b\u88e1\uff0c\u53ef\u4ee5\u6e05\u695a\u770b\u5230\u300c\u51fd\u5f0f\u4f5c\u7528\u57df\u300d\u639b\u540d\u4e00\u500b\u300c\u51fd\u5f0f\u300d\u524d\u7db4\u4e0d\u662f\u7a7a\u7a74\u4f86\u98a8\u7684\u3002",(0,r.jsx)(n.br,{}),"\n","\u51fd\u5f0f\u4f5c\u7528\u57df\u7684\u610f\u601d\u8868\u793a\u8b8a\u6578\u7684\u4f5c\u7528\u7bc4\u570d\u53ea\u9650\u65bc\u300c\u51fd\u5f0f\u5167\u90e8\u300d\u3002\u6240\u4ee5\u7576\u5916\u90e8 ",(0,r.jsx)(n.code,{children:"console.log"})," \u547c\u53eb ",(0,r.jsx)(n.code,{children:"name"})," \u6642\uff0c\u6703\u56e0\u70ba ",(0,r.jsx)(n.code,{children:"name"})," \u53ea\u5728\u51fd\u5f0f\u5167\u90e8\u5ba3\u544a\u800c\u5831\u932f\u3002",(0,r.jsx)(n.br,{}),"\n","\u563f\uff0c\u53ea\u505a\u7528\u5728\u300c\u51fd\u5f0f\u5167\u90e8\u300d\uff0c\u9019\u53e5\u8a71\u8d85\u91cd\u8981\u3002"]}),"\n",(0,r.jsx)(n.p,{children:"\u6240\u4ee5\u6211\u5011\u63db\u6210\u4e00\u500b\u4e0d\u662f\u51fd\u5f0f\u7684\u4f8b\u5b50\uff1a"}),"\n",(0,r.jsx)(n.pre,{children:(0,r.jsx)(n.code,{className:"language-javascript",children:"var isGirl = true\n\nif (isGirl) {\n var name = 'Jane'\n} else {\n var name = 'John'\n}\n\nconsole.log(name) // Jane\n"})}),"\n",(0,r.jsxs)(n.p,{children:["\u540c\u6a23\u7684 ",(0,r.jsx)(n.code,{children:"if"})," \u5224\u65b7\u5f0f\uff0c\u73fe\u5728\u628a ",(0,r.jsx)(n.code,{children:"var name"})," \u6539\u6210 ",(0,r.jsx)(n.code,{children:"let name"}),"\uff1a"]}),"\n",(0,r.jsx)(n.pre,{children:(0,r.jsx)(n.code,{className:"language-javascript",children:"var isGirl = true\nif (isGirl) {\n let name = 'Jane'\n} else {\n let name = 'John'\n}\n\nconsole.log(name) // ReferenceError: name is not defined\n"})}),"\n",(0,r.jsxs)(n.p,{children:["\u53ef\u4ee5\u770b\u5230\u5916\u90e8\u7684 ",(0,r.jsx)(n.code,{children:"console.log"})," \u5728 ",(0,r.jsx)(n.code,{children:"if"})," \u5167\u90e8\u8b8a\u6578\u5ba3\u544a\u6642\uff0c\u539f\u5148\u7528 ",(0,r.jsx)(n.code,{children:"var"})," \u7684\u60c5\u5f62\u53ef\u4ee5\u9806\u5229\u53d6\u5230\u503c\uff0c\u4f46\u6539\u6210 ",(0,r.jsx)(n.code,{children:"let"})," \u4e4b\u5f8c\u5674\u51fa\u4e86 ",(0,r.jsx)(n.code,{children:"ReferenceError"}),"\u3002",(0,r.jsx)(n.br,{}),"\n","\u9019\u5c31\u662f\u525b\u525b\u8aaa\u7684\u51fd\u5f0f\u4f5c\u7528\u57df\u53ea\u505a\u7528\u5728\u51fd\u5f0f\u5167\u90e8\u9019\u53e5\u8a71\u5f88\u91cd\u8981\uff0c",(0,r.jsx)(n.code,{children:"var"})," \u4e00\u5b9a\u5f97\u585e\u5728\u51fd\u5f0f\u88e1\u624d\u6703\u6709\u4f5c\u7528\u57df\u7684\u9650\u5236\u6548\u679c\uff0c\u5982\u679c\u653e\u5728\u5176\u4ed6\u5730\u65b9\u5c31\u6703\u88ab\u5ba3\u544a\u6210\u5168\u57df\u8b8a\u6578\u3002"]}),"\n",(0,r.jsxs)(n.p,{children:["\u90a3\u540c\u6a23\u4e0a\u8ff0\u4f8b\u5b50\u70ba\u4f55\u6539\u6210 ",(0,r.jsx)(n.code,{children:"let"})," \u4e4b\u5f8c\u5c31\u4e0d\u6703\u6709\u9019\u500b\u554f\u984c\uff1f",(0,r.jsx)(n.br,{}),"\n","\u773e\u6240\u5468\u77e5 ",(0,r.jsx)(n.code,{children:"let"})," \u548c ",(0,r.jsx)(n.code,{children:"const"})," \u662f\u300c\u5340\u584a\u4f5c\u7528\u57df\u300d\uff0c\u9019\u500b\u300c\u5340\u584a\u300d\u6307\u7684\u5c31\u662f ",(0,r.jsx)(n.code,{children:"{}"})," \u5305\u8d77\u4f86\u7684\u5340\u57df\uff0c\u5594\uff0c\u9019\u500b range \u5c31\u5f88\u5927\u4e86\u3002",(0,r.jsx)(n.br,{}),"\n","JavaScript \u88e1\u6700\u4e0d\u7f3a\u7684\u5c31\u662f\u7528 ",(0,r.jsx)(n.code,{children:"{}"})," \u5305\u8d77\u4f86\u7684\u5340\u57df\uff0c\u8209\u51e1 ",(0,r.jsx)(n.code,{children:"if"}),"\u3001",(0,r.jsx)(n.code,{children:"for"}),"\u3001",(0,r.jsx)(n.code,{children:"while"}),"\u3001",(0,r.jsx)(n.code,{children:"switch"})," \u7b49\u7b49\uff0c\u9019\u4e9b\u90fd\u6703\u88ab\u8996\u70ba\u5340\u584a\u3002",(0,r.jsx)(n.br,{}),"\n","\u56e0\u6b64\u5c0d\u4e0a\u8ff0\u4f8b\u5b50\u4f86\u8aaa\uff0c",(0,r.jsx)(n.code,{children:"let name"})," \u5df2\u7d93\u88ab\u9650\u5236\u53ea\u5728 ",(0,r.jsx)(n.code,{children:"if"})," \u5340\u584a\u5167\u90e8\u6709\u6548\uff0c\u5916\u90e8\u7684 ",(0,r.jsx)(n.code,{children:"console.log"})," \u7406\u6240\u7576\u7136\u5c31\u62ff\u4e0d\u5230\u503c\u3002"]}),"\n",(0,r.jsxs)(n.p,{children:["\u53e6\u4e00\u500b\u7d93\u5178\u7684\u4f8b\u5b50\u662f ",(0,r.jsx)(n.code,{children:"for"})," loop\uff0c\u9019\u500b\u65b0\u624b\u8d85\u7d1a\u5bb9\u6613\u5beb\u932f\u7684\uff1a"]}),"\n",(0,r.jsx)(n.pre,{children:(0,r.jsx)(n.code,{className:"language-javascript",children:"// Output: 3, 3, 3\nfor (var i = 0; i < 3;
1 i++) {\n setTimeout(() => {\n console.log(i)\n })\n}\n\n// Output: 0, 1, 2\nfor (let i = 0; i < 3; i++) {\n setTimeout(() => {\n console.log(i)\n })\n}\n"})}),"\n",(0,r.jsxs)(n.p,{children:["\u5728 ",(0,r.jsx)(n.code,{children:"for"})," loop \u88e1\u63d2\u9032\u4e00\u500b\u975e\u540c\u6b65\u7684 ",(0,r.jsx)(n.code,{children:"setTimeout"}),"\uff0c\u56e0\u70ba\u975e\u540c\u6b65\u7684\u7279\u6027\uff0c",(0,r.jsx)(n.code,{children:"setTimeout"})," \u6703\u7b49\u5230 ",(0,r.jsx)(n.code,{children:"for"})," loop \u8dd1\u5b8c\u624d\u57f7\u884c\u3002",(0,r.jsx)(n.br,{}),"\n","\u5728\u7528 ",(0,r.jsx)(n.code,{children:"var"})," \u5ba3\u544a\u7684\u60c5\u6cc1\u4e0b\uff0c",(0,r.jsx)(n.code,{children:"i"})," \u662f\u88ab\u5ba3\u544a\u6210\u5168\u57df\u4f5c\u7528\u57df\uff0c\u6240\u4ee5 ",(0,r.jsx)(n.code,{children:"for"})," loop \u6bcf\u6b21\u5faa\u74b0\u62ff\u7684\u90fd\u662f\u540c\u4e00\u500b ",(0,r.jsx)(n.code,{children:"i"}),"\uff0c\u7b49\u5230 ",(0,r.jsx)(n.code,{children:"setTimeout"})," \u57f7\u884c\u6642\uff0c",(0,r.jsx)(n.code,{children:"i"})," \u7684\u503c\u5df2\u7d93\u662f 3 \u4e86\uff0c\u6240\u4ee5\u8f38\u51fa\u90fd\u662f 3\u3002",(0,r.jsx)(n.br,{}),"\n","\u4f46\u7528 ",(0,r.jsx)(n.code,{children:"let"})," \u5c31\u4e0d\u4e00\u6a23\u4e86\uff0c\u5c0d ",(0,r.jsx)(n.code,{children:"let"})," \u4f86\u8aaa\uff0c\u6bcf\u500b ",(0,r.jsx)(n.code,{children:"for"})," loop \u5faa\u74b0\u90fd\u662f\u5efa\u7acb\u4e00\u500b\u65b0\u7684\u5340\u584a\uff0c\u6240\u4ee5\u4ed6\u4e09\u6b21\u53d6\u5230\u7684 ",(0,r.jsx)(n.code,{children:"i"})," \u90fd\u662f\u7368\u7acb\u7684\uff0c\u6c92\u6709\u50cf ",(0,r.jsx)(n.code,{children:"var"})," \u767c\u751f\u90a3\u7a2e\u5168\u57df\u5171\u7528\u56e0\u6b64\u88ab\u6539\u4e09\u6b21\u7684\u60c5\u5f62\uff0c\u6240\u4ee5\u8f38\u51fa\u5c31\u662f 0\u30011\u30012\u3002"]}),"\n",(0,r.jsxs)(n.admonition,{type:"info",children:[(0,r.jsx)(n.p,{children:"\u56b4\u683c\u4f86\u8b1b\uff0c\u9084\u6709\u4e00\u7a2e\u60c5\u6cc1\u53ef\u4ee5\u63a2\u8a0e\uff0c\u5c31\u662f\u6c92\u6709\u5ba3\u544a\u8b8a\u6578\u7684\u60c5\u6cc1\u3002"}),(0,r.jsx)(n.pre,{children:(0,r.jsx)(n.code,{children:"a = 3\nconsole.log(a)\n"})}),(0,r.jsxs)(n.p,{children:["\u9019\u6a23\u7684\u60c5\u6cc1\u4e0b\uff0c",(0,r.jsx)(n.code,{children:"a"})," \u6703\u88ab\u5ba3\u544a\u70ba\u5168\u57df\u8b8a\u6578 (\u56b4\u683c\u4e00\u9ede\u8aaa\u662f\u5168\u57df\u5c6c\u6027\uff0cno mind\uff0c\u9019\u88e1\u4e0d\u7528\u63a2\u8a0e\u90a3\u9ebc\u7d30)\u3002",(0,r.jsx)(n.br,{}),"\n","\u4e0d\u628a\u4e0d\u5ba3\u544a\u8b8a\u6578\u9019\u4ef6\u4e8b\u62ce\u51fa\u4f86\u8b1b\uff0c\u662f\u56e0\u70ba\u5be6\u52d9\u4e3b\u6d41\u958b\u767c\u6642\u4f7f\u7528\u7684\u6846\u67b6\u6216 library\uff0cVue \u4e5f\u597d\u3001React \u4e5f\u597d\uff0c\u5176\u5be6\u57fa\u672c\u90fd\u662f strict mode\uff0c\u6703\u5c0d\u9019\u7a2e\u6c92\u5ba3\u544a\u76f4\u63a5\u5f15\u7528\u7684\u60c5\u6cc1\u5674 error\u3002",(0,r.jsx)(n.br,{}),"\n","\u60f3\u73a9\u9019\u7a2e\u60c5\u5f62\u5927\u6982\u5c31\u662f VScode \u81ea\u5df1\u958b\u652f JS \u6a94\u6848\u6216\u53bb devtool \u73a9\u73a9\u3002"]})]}),"\n",(0,r.jsxs)(n.admonition,{type:"tip",children:[(0,r.jsxs)(n.ol,{children:["\n",(0,r.jsx)(n.li,{children:"\u56b4\u683c\u4e0a\u4f86\u8aaa\uff0c\u5168\u57df\u8b8a\u6578\u8ddf\u5168\u57df\u5c6c\u6027\u9084\u662f\u7a0d\u5fae\u6709\u5dee\u7684\uff0c\u4f46\u500b\u4eba\u8a8d\u70ba\u7406\u89e3\u5230\u5168\u57df\u8b8a\u6578\u5c31\u975e\u5e38\u8db3\u5920\u4e86\uff0c\u5168\u57df\u5c6c\u6027\u5c31\u662f\u500b\u6dfb\u982d\u3002\u771f\u7684\u60f3\u77e5\u9053\u7684\u8a71\u5efa\u8b70\u9084\u662f\u8b80\u4e00\u4e0b\u5361\u65af\u4f2f\u7684\u66f8\u3002"}),"\n",(0,r.jsxs)(n.li,{children:["\u601d\u4f86\u60f3\u53bb\uff0c\u9084\u662f\u5beb\u4e00\u4e0b ",(0,r.jsx)(n.code,{children:"let"})," \u8ddf ",(0,r.jsx)(n.code,{children:"const"})," \u7684\u5dee\u5225"]}),"\n"]}),(0,r.jsxs)(n.ul,{children:["\n",(0,r.jsxs)(n.li,{children:[(0,r.jsx)(n.code,{children:"let"}),"\uff1a\u7528\u5728\u5ba3\u544a\u53ef\u4ee5\u91cd\u65b0\u8ce6\u503c\u7684\u8b8a\u6578\u3002"]}),"\n",(0,r.jsxs)(n.li,{children:[(0,r.jsx)(n.code,{children:"const"}),"\uff1a\u7528\u5728\u5ba3\u544a\u4e0d\u53ef\u91cd\u65b0\u8ce6\u503c\u7684\u8b8a\u6578\uff0c\u4e5f\u5c31\u662f\u5e38\u6578\u3002\u984d\u5916\u4e00\u63d0\uff0c\u7528 ",(0,r.jsx)(n.code,{children:"const"})," \u5ba3\u544a\u7269\u4ef6\u6216\u9663\u5217\u662f\u53ef\u4ee5\u900f\u904e\u7269\u4ef6\u65b9\u6cd5 (e.g., ",(0,r.jsx)(n.code,{children:"obj.key = ..."}),") \u6216\u9663\u5217\u65b9\u6cd5 (e.g., ",(0,r.jsx)(n.code,{children:"push()"}),") \u6539\u8b8a\u5176\u5167\u90e8\u7684\u503c\u7684\u3002"]}),"\n"]})]}),"\n",(0,r.jsx)(n.h2,{id:"\u63d0\u5347-hoisting",children:"\u63d0\u5347 (Hoisting)"}),"\n",(0,r.jsxs)(n.p,{children:["\u90fd\u63d0\u5230 ",(0,r.jsx)(n.code,{children:"var"}),"\u3001",(0,r.jsx)(n.code,{children:"let"}),"\u3001",(0,r.jsx)(n.code,{children:"const"})," \u7b49\u5ba3\u544a\u8b8a\u6578\u7684\u65b9\u5f0f\u4e86\uff0c\u90a3\u4e0d\u53ef\u907f\u514d\u5730\u5f97\u4f86\u804a\u804a\u4e00\u4e9b\u95dc\u65bc\u300c\u63d0\u5347 (Hoisting)\u300d\u7684\u8a71\u984c\u3002",(0,r.jsx)(n.br,{}
1),"\n","\u63d0\u5347\u5728 JavaScript \u4e2d\u7e3d\u5171\u6709\u5169\u500b\u5730\u65b9\u6703\u63a2\u8a0e\u5230\uff1a"]}),"\n",(0,r.jsxs)(n.ol,{children:["\n",(0,r.jsx)(n.li,{children:"\u8b8a\u6578\u7684\u5ba3\u544a"}),"\n",(0,r.jsx)(n.li,{children:"\u51fd\u5f0f\u7684\u5ba3\u544a"}),"\n"]}),"\n",(0,r.jsx)(n.p,{children:"\u63a2\u8a0e\u7684\u90fd\u662f\u4e00\u500b\u9806\u5e8f\u4e0a\u7684\u884c\u70ba\uff1a"}),"\n",(0,r.jsxs)(n.blockquote,{children:["\n",(0,r.jsx)(n.p,{children:"\u80fd\u4e0d\u80fd\u5728\u5ba3\u544a\u8b8a\u6578 / \u51fd\u5f0f\u4e4b\u524d\u5c31\u8abf\u7528\u4ed6\u5011\uff1f"}),"\n"]}),"\n",(0,r.jsxs)(n.p,{children:["\u51fd\u5f0f\u7684\u63d0\u5347\u6211\u5011\u59d1\u4e14\u653e\u5230\u65e5\u5f8c\u518d\u8ac7\uff0c\u9019\u73a9\u610f\u5152\u727d\u626f\u5230\u4e00\u822c ",(0,r.jsx)(n.code,{children:"function"})," \u5ba3\u544a\u8207 arrow function \u7684\u5dee\u7570\u3002",(0,r.jsx)(n.br,{}),"\n","\u9019\u88e1\u6211\u5011\u5c31\u5c08\u6ce8\u5728\u8b8a\u6578\u7684\u63d0\u5347\u5c31\u597d\u3002",(0,r.jsx)(n.br,{}),"\n","\u90a3\u6211\u5011\u628a\u554f\u984c narrow \u4e00\u4e0b\uff1a"]}),"\n",(0,r.jsxs)(n.blockquote,{children:["\n",(0,r.jsx)(n.p,{children:"\u80fd\u4e0d\u80fd\u5728\u5ba3\u544a\u8b8a\u6578\u4e4b\u524d\u5c31\u8abf\u7528\u4ed6\u5011\uff1f"}),"\n"]}),"\n",(0,r.jsxs)(n.p,{children:["\u76f4\u63a5\u8aaa\u7d50\u8ad6\uff1a\u53ef\u4ee5\uff0c\u4f46\u9650\u65bc\u7528 ",(0,r.jsx)(n.code,{children:"var"})," \u5ba3\u544a\u8b8a\u6578\u3002"]}),"\n",(0,r.jsx)(n.pre,{children:(0,r.jsx)(n.code,{className:"language-javascript",metastring:'title="use var"',children:'console.log(name) // undefined\nvar name = "Jack"\n'})}),"\n",(0,r.jsx)(n.pre,{children:(0,r.jsx)(n.code,{className:"language-javascript",metastring:'title="use let"',children:'console.log(name) // ReferenceError: name is not defined\nlet name = "Jack"\n'})}),"\n",(0,r.jsxs)(n.p,{children:["\u53ef\u4ee5\u6e05\u695a\u770b\u5230\u7528 ",(0,r.jsx)(n.code,{children:"var"})," \u5ba3\u544a\u8ddf\u7528 ",(0,r.jsx)(n.code,{children:"let"})," (or ",(0,r.jsx)(n.code,{children:"const"}),") \u5ba3\u544a\u5674\u51fa\u7684 error \u4e0d\u4e00\u6a23\u3002"]}),"\n",(0,r.jsxs)(n.ol,{children:["\n",(0,r.jsxs)(n.li,{children:[(0,r.jsx)(n.code,{children:"var"}),"\uff1a\u5f97\u5230 ",(0,r.jsx)(n.code,{children:"undefined"}),"\uff0c\u9019\u662f\u627e\u4e0d\u5230\u8b8a\u6578\u503c\u7684 error\uff0c\u767c\u751f\u539f\u56e0\u7b49\u4e0b\u63d0\u3002"]}),"\n",(0,r.jsxs)(n.li,{children:[(0,r.jsx)(n.code,{children:"let"})," (or ",(0,r.jsx)(n.code,{children:"const"}),")\uff1a\u5f97\u5230 ",(0,r.jsx)(n.code,{children:"ReferenceError"}),"\uff0c\u9019\u662f\u627e\u4e0d\u5230\u8b8a\u6578\u7684\u5ba3\u544a\u3002"]}),"\n"]}),"\n",(0,r.jsxs)(n.p,{children:["\u751a\u81f3 ",(0,r.jsx)(n.code,{children:"let"})," \u90a3\u9805\u7bc4\u4f8b\u9084\u6703\u6709\u500b\u984d\u5916\u63d0\u793a\uff0c\u300cReferenceError: Cannot access 'name' before initialization\u300d\uff0c\u7121\u4e00\u4e0d\u90fd\u662f\u5728\u8aaa\u660e ",(0,r.jsx)(n.code,{children:"let"})," \u6216 ",(0,r.jsx)(n.code,{children:"const"})," \u7981\u6b62\u5728\u5ba3\u544a\u4e4b\u524d\u4f7f\u7528\u8b8a\u6578\u3002",(0,r.jsx)(n.br,{}),"\n","\u76f8\u6bd4\u4e4b\u4e0b\uff0c",(0,r.jsx)(n.code,{children:"var"})," \u5c31\u597d\u50cf\u90a3\u81ea\u7531\u7684\u9ce5\u5152\uff0c\u600e\u9ebc\u81ea\u7531\u600e\u9ebc\u4f86\uff0c\u53ef\u4ee5\u770b\u5230\u5373\u4f7f\u5b83\u5ba3\u544a\u5728\u8abf\u7528\u4e4b\u524d\uff0c\u8abf\u7528\u5b83\u7684 ",(0,r.jsx)(n.code,{children:"console.log"})," \u4ecd\u7136\u53ef\u4ee5\u6293\u5230\u4ed6\uff0c\u9019\u6642\u6211\u5011\u5c31\u53ef\u4ee5\u8aaa\u8b8a\u6578\u300c\u63d0\u5347\u300d\u5230\u8abf\u7528\u7684\u5b83\u7684\u9805\u76ee\u4e4b\u524d\u4e86\u3002"]}),"\n",(0,r.jsxs)(n.p,{children:["\u81f3\u65bc\u70ba\u4f55 ",(0,r.jsx)(n.code,{children:"var"})," \u7684\u7bc4\u4f8b\u6703\u5f97\u5230 ",(0,r.jsx)(n.code,{children:"undefined"}),"\uff0c\u9019\u5c31\u662f\u63d0\u5347\u7684\u53e6\u4e00\u500b\u6982\u5ff5\uff1a"]}),"\n",(0,r.jsxs)(n.blockquote,{children:["\n",(0,r.jsx)(n.p,{children:"\u63d0\u5347\u662f\u6307\u628a\u8b8a\u6578\u7684\u5ba3\u544a\u653e\u5230\u4f5c\u7528\u57df\u7684\u6700\u4e0a\u9762\uff0c\u4f46\u4e0d\u6703\u9023\u540c\u8ce6\u503c\u4e00\u8d77\u63d0\u5347\u3002"}),"\n"]}),"\n",(0,r.jsx)(n.p,{children:"\u807d\u8d77\u4f86\u6709\u9ede\u62bd\u8c61\uff0c\u4f46\u770b\u4e00\u4e0b\u4e0a\u9762\u7bc4\u4f8b\u63d0\u5347\u5f8c\u7684\u6a23\u5b50\u5c31\u6e05\u695a\u4e86\uff1a"}),"\n",(0,r.jsx)(n.pre,{children:(0,r.jsx)(n.code,{className:"language-javascript",children:'var name // \u5ba3\u544a\u88ab\u63d0\u5347\u5230\u6700\u4e0a\u9762\nconsole.log(name) // undefined\nname = "Jack" // \u8ce6\u503c\u6c92\u6709\u88ab\u63d0\u5347\n'})}),"\n",(0,r.jsxs)(n.p,{children:["\u56e0\u70ba\u7fd2\u6163\u4e0a\u6211\u5011\u5e38\u6703\u
1628a\u5ba3\u544a\u8b8a\u6578\u8207\u8ce6\u503c\u653e\u5728\u4e00\u8d77\u5beb\uff0c\u8a31\u591a\u65b0\u624b\u5c31\u6703\u628a\u5b83\u7576\u4f5c\u662f\u4e00\u4ef6\u4e8b\u4f86\u770b\uff0c\u4f46\u5be6\u969b\u4e0a\u300c\u5ba3\u544a\u300d\u8207\u300c\u8ce6\u503c\u300d\u662f\u5169\u500b\u7368\u7acb\u7684\u4e8b\u4ef6\u3002",(0,r.jsx)(n.br,{}),"\n","\u4e0a\u9762\u9019\u662f ",(0,r.jsx)(n.code,{children:'var name = "Jack"'})," \u7684\u63d0\u5347\u5f8c\u6a23\u5b50\uff0c\u5ba3\u544a\u88ab\u63d0\u5347\u5230\u6700\u4e0a\u9762\uff0c\u4f46\u8ce6\u503c\u6c92\u6709\u88ab\u63d0\u5347\uff0c\u56e0\u6b64 ",(0,r.jsx)(n.code,{children:"console.log(name)"})," \u6703\u5f97\u5230 ",(0,r.jsx)(n.code,{children:"undefined"}),"\u3002"]}),"\n",(0,r.jsx)(n.admonition,{type:"info",children:(0,r.jsxs)(n.p,{children:["\u5176\u5be6\u56b4\u683c\u4e00\u9ede\u4f86\u8b1b\uff0c",(0,r.jsx)(n.code,{children:"let"})," \u8207 ",(0,r.jsx)(n.code,{children:"const"})," \u662f\u6703\u63d0\u5347\u7684\uff0c\u53ea\u662f\u4ed6\u5011\u6703\u9677\u5165\u4e00\u500b\u53eb\u505a\u300c\u66ab\u6642\u6027\u6b7b\u5340 (Temporal Dead Zone, TDZ)\u300d\u3002",(0,r.jsx)(n.br,{}),"\n","TDZ \u8b1b\u7684\u662f JavaScript \u62d2\u7d55\u5728\u8ce6\u503c\u4e4b\u524d\u4f7f\u7528\u8b8a\u6578\uff0c\u800c\u5982\u524d\u8ff0\u6240\u8aaa\uff0c\u63d0\u5347\u4e26\u4e0d\u6703\u63d0\u5347\u8ce6\u503c\uff0c\u6240\u4ee5\u5373\u4f7f ",(0,r.jsx)(n.code,{children:"let"})," \u8207 ",(0,r.jsx)(n.code,{children:"const"})," \u7684\u5ba3\u544a\u88ab\u63d0\u5347\u4e86\uff0c\u4f46\u7121\u53ef\u907f\u514d\u5730\u4e00\u5b9a\u6703\u8e29\u5165 TDZ\uff0c\u9032\u800c\u5674\u51fa ",(0,r.jsx)(n.code,{children:"ReferenceError"}),"\u3002",(0,r.jsx)(n.br,{}),"\n","\u4e45\u800c\u4e45\u4e4b\uff0c",(0,r.jsx)(n.code,{children:"let"})," \u8207 ",(0,r.jsx)(n.code,{children:"const"})," \u5c31\u53ef\u4ee5\u7576\u6210\u6c92\u6709\u63d0\u5347\u4f86\u770b\u5f85\u3002"]})})]})}function j(e={}){const{wrapper:n}={...(0,i.R)(),...e.components};return n?(0,r.jsx)(n,{...e,children:(0,r.jsx)(t,{...e})}):t(e)}}}]);
Line numbers count LF bytes from the start of the resource, as the search results do. Vendor segments are library code the classifier recognised; they are stored but not indexed. Bytes are shown as Latin1 characters, one per byte.