{"id":2025,"date":"2025-02-25T22:29:17","date_gmt":"2025-02-25T14:29:17","guid":{"rendered":"https:\/\/www.laixuexila.com\/?p=2025"},"modified":"2025-02-25T22:29:17","modified_gmt":"2025-02-25T14:29:17","slug":"javascript-%e4%bd%9c%e7%94%a8%e5%9f%9f","status":"publish","type":"post","link":"https:\/\/www.laixuexila.com\/index.php\/2025\/02\/25\/javascript-%e4%bd%9c%e7%94%a8%e5%9f%9f\/","title":{"rendered":"JavaScript \u4f5c\u7528\u57df"},"content":{"rendered":"\n<p>\u5728 JavaScript \u4e2d\uff0c<strong>\u4f5c\u7528\u57df\uff08Scope\uff09<\/strong> \u662f\u6307\u53d8\u91cf\u3001\u51fd\u6570\u548c\u5bf9\u8c61\u7684\u53ef\u8bbf\u95ee\u8303\u56f4\u3002\u5b83\u51b3\u5b9a\u4e86\u5982\u4f55\u67e5\u627e\u53d8\u91cf\u4ee5\u53ca\u5728\u4e0d\u540c\u7684\u4ee3\u7801\u5757\u4e2d\uff0c\u54ea\u4e9b\u53d8\u91cf\u662f\u53ef\u89c1\u7684\u3002\u7406\u89e3\u4f5c\u7528\u57df\u662f\u7406\u89e3 JavaScript \u6267\u884c\u4e0a\u4e0b\u6587\u548c\u53d8\u91cf\u751f\u547d\u5468\u671f\u7684\u5173\u952e\u3002<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">1. <strong>\u5168\u5c40\u4f5c\u7528\u57df\uff08Global Scope\uff09<\/strong><\/h3>\n\n\n\n<p>\u5168\u5c40\u4f5c\u7528\u57df\u6307\u7684\u662f\u5728\u4ee3\u7801\u7684\u6700\u5916\u5c42\u5b9a\u4e49\u7684\u53d8\u91cf\u548c\u51fd\u6570\u3002\u5b83\u4eec\u5728\u6574\u4e2a\u5e94\u7528\u7a0b\u5e8f\u4e2d\u90fd\u53ef\u4ee5\u8bbf\u95ee\u3002<\/p>\n\n\n\n<h4 class=\"wp-block-heading\">\u4f8b\u5b50\uff1a<\/h4>\n\n\n\n<pre class=\"wp-block-code\"><code>let globalVar = \"I am global\";\n\nfunction greet() {\n  console.log(globalVar);  \/\/ \u53ef\u4ee5\u8bbf\u95ee\u5168\u5c40\u53d8\u91cf\n}\n\ngreet();  \/\/ \u8f93\u51fa\uff1aI am global\nconsole.log(globalVar);  \/\/ \u8f93\u51fa\uff1aI am global<\/code><\/pre>\n\n\n\n<p>\u5728\u4e0a\u9762\u7684\u4f8b\u5b50\u4e2d\uff0c<code>globalVar<\/code> \u5b9a\u4e49\u5728\u5168\u5c40\u4f5c\u7528\u57df\u4e2d\uff0c\u6240\u4ee5\u5b83\u5728 <code>greet()<\/code> \u51fd\u6570\u5185\u5916\u90fd\u53ef\u7528\u3002<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">2. <strong>\u51fd\u6570\u4f5c\u7528\u57df\uff08Function Scope\uff09<\/strong><\/h3>\n\n\n\n<p>\u6bcf\u4e2a\u51fd\u6570\u90fd\u6709\u81ea\u5df1\u7684\u4f5c\u7528\u57df\u3002\u51fd\u6570\u5185\u90e8\u7684\u53d8\u91cf\u548c\u51fd\u6570\u53ea\u80fd\u5728\u8be5\u51fd\u6570\u5185\u8bbf\u95ee\uff0c\u5916\u90e8\u65e0\u6cd5\u8bbf\u95ee\u3002<\/p>\n\n\n\n<h4 class=\"wp-block-heading\">\u4f8b\u5b50\uff1a<\/h4>\n\n\n\n<pre class=\"wp-block-code\"><code>function greet() {\n  let localVar = \"I am local\";  \/\/ \u51fd\u6570\u5185\u90e8\u7684\u53d8\u91cf\n  console.log(localVar);  \/\/ \u53ef\u4ee5\u8bbf\u95ee\n}\n\ngreet();  \/\/ \u8f93\u51fa\uff1aI am local\nconsole.log(localVar);  \/\/ \u62a5\u9519\uff1aUncaught ReferenceError: localVar is not defined<\/code><\/pre>\n\n\n\n<p>\u5728\u4e0a\u9762\u7684\u4f8b\u5b50\u4e2d\uff0c<code>localVar<\/code> \u662f\u4e00\u4e2a\u5728 <code>greet()<\/code> \u51fd\u6570\u5185\u90e8\u58f0\u660e\u7684\u53d8\u91cf\uff0c\u56e0\u6b64\u53ea\u80fd\u5728\u51fd\u6570\u5185\u90e8\u8bbf\u95ee\uff0c\u5728\u5916\u90e8\u8bbf\u95ee\u65f6\u4f1a\u629b\u51fa\u9519\u8bef\u3002<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">3. <strong>\u5757\u7ea7\u4f5c\u7528\u57df\uff08Block Scope\uff09<\/strong><\/h3>\n\n\n\n<p>\u5757\u7ea7\u4f5c\u7528\u57df\u662f\u6307\u5728 <code>{}<\/code> \u5185\u90e8\u5b9a\u4e49\u7684\u4f5c\u7528\u57df\u3002\u4f7f\u7528 <code>let<\/code> \u548c <code>const<\/code> \u5173\u952e\u5b57\u58f0\u660e\u7684\u53d8\u91cf\u6709\u5757\u7ea7\u4f5c\u7528\u57df\uff0c\u5b83\u4eec\u53ea\u80fd\u5728\u58f0\u660e\u5b83\u4eec\u7684\u4ee3\u7801\u5757\u5185\u8bbf\u95ee\u3002<code>var<\/code> \u58f0\u660e\u7684\u53d8\u91cf\u5219\u6ca1\u6709\u5757\u7ea7\u4f5c\u7528\u57df\uff0c\u800c\u662f\u5c5e\u4e8e\u51fd\u6570\u4f5c\u7528\u57df\u6216\u5168\u5c40\u4f5c\u7528\u57df\u3002<\/p>\n\n\n\n<h4 class=\"wp-block-heading\">\u4f8b\u5b50\uff1a<\/h4>\n\n\n\n<pre class=\"wp-block-code\"><code>if (true) {\n  let blockVar = \"I am in block\";\n  console.log(blockVar);  \/\/ \u8f93\u51fa\uff1aI am in block\n}\n\nconsole.log(blockVar);  \/\/ \u62a5\u9519\uff1aUncaught ReferenceError: blockVar is not defined<\/code><\/pre>\n\n\n\n<p>\u5728\u4e0a\u9762\u7684\u4f8b\u5b50\u4e2d\uff0c<code>blockVar<\/code> \u53ea\u80fd\u5728 <code>if<\/code> \u8bed\u53e5\u7684\u4ee3\u7801\u5757\u5185\u8bbf\u95ee\uff0c\u5916\u90e8\u65e0\u6cd5\u8bbf\u95ee\u5b83\u3002<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">4. <strong>\u4f5c\u7528\u57df\u94fe\uff08Scope Chain\uff09<\/strong><\/h3>\n\n\n\n<p>\u4f5c\u7528\u57df\u94fe\u662f\u7531\u591a\u4e2a\u4f5c\u7528\u57df\u7ec4\u6210\u7684\u94fe\u6761\u3002\u5f53\u8bbf\u95ee\u4e00\u4e2a\u53d8\u91cf\u65f6\uff0cJavaScript \u5f15\u64ce\u4f1a\u4ece\u5f53\u524d\u4f5c\u7528\u57df\u5f00\u59cb\u67e5\u627e\uff0c\u5982\u679c\u6ca1\u6709\u627e\u5230\u5c31\u4f1a\u67e5\u627e\u5916\u90e8\u4f5c\u7528\u57df\uff0c\u4e00\u76f4\u5230\u5168\u5c40\u4f5c\u7528\u57df\u4e3a\u6b62\u3002<\/p>\n\n\n\n<h4 class=\"wp-block-heading\">\u4f8b\u5b50\uff1a<\/h4>\n\n\n\n<pre class=\"wp-block-code\"><code>let globalVar = \"I am global\";\n\nfunction outerFunction() {\n  let outerVar = \"I am outer\";\n\n  function innerFunction() {\n    let innerVar = \"I am inner\";\n    console.log(innerVar);  \/\/ \u8bbf\u95ee\u5185\u5c42\u53d8\u91cf\n    console.log(outerVar);  \/\/ \u8bbf\u95ee\u5916\u5c42\u51fd\u6570\u7684\u53d8\u91cf\n    console.log(globalVar); \/\/ \u8bbf\u95ee\u5168\u5c40\u53d8\u91cf\n  }\n\n  innerFunction();\n}\n\nouterFunction();<\/code><\/pre>\n\n\n\n<p><strong>\u8f93\u51fa\uff1a<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>I am inner\nI am outer\nI am global<\/code><\/pre>\n\n\n\n<p>\u5728\u4e0a\u9762\u7684\u4f8b\u5b50\u4e2d\uff0c<code>innerFunction<\/code> \u53ef\u4ee5\u8bbf\u95ee\u81ea\u5df1\u7684\u4f5c\u7528\u57df\u4e2d\u7684\u53d8\u91cf <code>innerVar<\/code>\uff0c\u540c\u65f6\u4e5f\u80fd\u8bbf\u95ee <code>outerFunction<\/code> \u4e2d\u7684 <code>outerVar<\/code> \u4ee5\u53ca\u5168\u5c40\u4f5c\u7528\u57df\u4e2d\u7684 <code>globalVar<\/code>\u3002\u8fd9\u662f\u56e0\u4e3a <code>innerFunction<\/code> \u7684\u4f5c\u7528\u57df\u94fe\u5305\u62ec\u4e86\u5176\u81ea\u8eab\u4f5c\u7528\u57df\u3001<code>outerFunction<\/code> \u7684\u4f5c\u7528\u57df\u4ee5\u53ca\u5168\u5c40\u4f5c\u7528\u57df\u3002<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">5. <strong>\u95ed\u5305\uff08Closure\uff09<\/strong><\/h3>\n\n\n\n<p>\u95ed\u5305\u662f JavaScript \u4e2d\u7684\u4e00\u4e2a\u91cd\u8981\u6982\u5ff5\uff0c\u5b83\u662f\u6307\u51fd\u6570\u53ef\u4ee5\u8bbf\u95ee\u5176\u5916\u90e8\u51fd\u6570\u4f5c\u7528\u57df\u4e2d\u7684\u53d8\u91cf\uff0c\u5373\u4f7f\u5916\u90e8\u51fd\u6570\u5df2\u7ecf\u8fd4\u56de\u3002\u95ed\u5305\u5141\u8bb8\u51fd\u6570\u5728\u5176\u5916\u90e8\u4f5c\u7528\u57df\u7684\u73af\u5883\u4e2d\u4fdd\u6301\u5bf9\u53d8\u91cf\u7684\u5f15\u7528\u3002<\/p>\n\n\n\n<h4 class=\"wp-block-heading\">\u4f8b\u5b50\uff1a<\/h4>\n\n\n\n<pre class=\"wp-block-code\"><code>function outerFunction() {\n  let outerVar = \"I am outer\";\n\n  return function innerFunction() {\n    console.log(outerVar);  \/\/ innerFunction \u8bbf\u95ee\u5916\u90e8\u51fd\u6570\u7684\u53d8\u91cf\n  };\n}\n\nlet closureFunction = outerFunction();  \/\/ \u8fd4\u56de\u5185\u5c42\u51fd\u6570\nclosureFunction();  \/\/ \u8f93\u51fa\uff1aI am outer<\/code><\/pre>\n\n\n\n<p>\u5728\u4e0a\u9762\u7684\u4f8b\u5b50\u4e2d\uff0c<code>innerFunction<\/code> \u662f\u4e00\u4e2a\u95ed\u5305\uff0c\u5b83\u53ef\u4ee5\u8bbf\u95ee <code>outerFunction<\/code> \u4e2d\u7684 <code>outerVar<\/code> \u53d8\u91cf\uff0c\u5373\u4f7f <code>outerFunction<\/code> \u5df2\u7ecf\u8fd4\u56de\uff0c<code>outerVar<\/code> \u4f9d\u7136\u5728 <code>innerFunction<\/code> \u4e2d\u53ef\u7528\u3002<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">6. <strong>\u53d8\u91cf\u63d0\u5347\uff08Hoisting\uff09<\/strong><\/h3>\n\n\n\n<p>\u53d8\u91cf\u63d0\u5347\u662f JavaScript \u4e2d\u7684\u4e00\u79cd\u884c\u4e3a\uff0c\u5728\u6267\u884c\u4ee3\u7801\u4e4b\u524d\uff0c\u6240\u6709\u7684 <code>var<\/code> \u58f0\u660e\u4f1a\u88ab\u63d0\u5347\u5230\u51fd\u6570\u6216\u5168\u5c40\u4f5c\u7528\u57df\u7684\u9876\u90e8\uff0c\u4f46\u4e0d\u4f1a\u63d0\u5347\u8d4b\u503c\u64cd\u4f5c\u3002<\/p>\n\n\n\n<h4 class=\"wp-block-heading\">\u4f8b\u5b50\uff1a<\/h4>\n\n\n\n<pre class=\"wp-block-code\"><code>console.log(myVar);  \/\/ \u8f93\u51fa\uff1aundefined\nvar myVar = 10;\nconsole.log(myVar);  \/\/ \u8f93\u51fa\uff1a10<\/code><\/pre>\n\n\n\n<p>\u5728\u4e0a\u9762\u7684\u4f8b\u5b50\u4e2d\uff0c<code>myVar<\/code> \u88ab\u63d0\u5347\u5230\u4f5c\u7528\u57df\u7684\u9876\u90e8\uff0c\u4f46\u5b83\u7684\u503c\u8d4b\u4e3a <code>10<\/code> \u7684\u64cd\u4f5c\u4fdd\u6301\u5728\u539f\u5730\u3002\u56e0\u6b64\u7b2c\u4e00\u6b21 <code>console.log(myVar)<\/code> \u8f93\u51fa <code>undefined<\/code>\uff0c\u7b2c\u4e8c\u6b21\u8f93\u51fa <code>10<\/code>\u3002<\/p>\n\n\n\n<p>\u5bf9\u4e8e <code>let<\/code> \u548c <code>const<\/code>\uff0c\u867d\u7136\u5b83\u4eec\u4e5f\u4f1a\u88ab\u63d0\u5347\uff0c\u4f46\u5b83\u4eec\u4e0d\u4f1a\u88ab\u521d\u59cb\u5316\uff0c\u76f4\u5230\u4ee3\u7801\u6267\u884c\u5230\u76f8\u5e94\u7684\u4f4d\u7f6e\u3002\u8bbf\u95ee\u5b83\u4eec\u4f1a\u629b\u51fa\u9519\u8bef\u3002<\/p>\n\n\n\n<h4 class=\"wp-block-heading\">\u4f8b\u5b50\uff1a<\/h4>\n\n\n\n<pre class=\"wp-block-code\"><code>console.log(myVar);  \/\/ \u62a5\u9519\uff1aUncaught ReferenceError: Cannot access 'myVar' before initialization\nlet myVar = 10;<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\">7. <strong>\u603b\u7ed3<\/strong><\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>\u5168\u5c40\u4f5c\u7528\u57df<\/strong>\uff1a\u6700\u5916\u5c42\u7684\u4f5c\u7528\u57df\uff0c\u4ee3\u7801\u4e2d\u672a\u5d4c\u5957\u5728\u4efb\u4f55\u51fd\u6570\u5185\u7684\u90e8\u5206\u3002<\/li>\n\n\n\n<li><strong>\u51fd\u6570\u4f5c\u7528\u57df<\/strong>\uff1a\u51fd\u6570\u5185\u90e8\u7684\u4f5c\u7528\u57df\uff0c\u51fd\u6570\u5185\u90e8\u5b9a\u4e49\u7684\u53d8\u91cf\u53ea\u80fd\u5728\u51fd\u6570\u5185\u8bbf\u95ee\u3002<\/li>\n\n\n\n<li><strong>\u5757\u7ea7\u4f5c\u7528\u57df<\/strong>\uff1a\u7531 <code>{}<\/code> \u5305\u88f9\u7684\u533a\u57df\uff0c<code>let<\/code> \u548c <code>const<\/code> \u58f0\u660e\u7684\u53d8\u91cf\u5177\u6709\u5757\u7ea7\u4f5c\u7528\u57df\u3002<\/li>\n\n\n\n<li><strong>\u4f5c\u7528\u57df\u94fe<\/strong>\uff1a\u901a\u8fc7\u94fe\u5f0f\u67e5\u627e\u673a\u5236\u67e5\u627e\u53d8\u91cf\uff0c\u4f9d\u6b21\u4ece\u5f53\u524d\u4f5c\u7528\u57df\u5230\u5916\u90e8\u4f5c\u7528\u57df\u76f4\u5230\u5168\u5c40\u4f5c\u7528\u57df\u3002<\/li>\n\n\n\n<li><strong>\u95ed\u5305<\/strong>\uff1a\u51fd\u6570\u53ef\u4ee5\u4fdd\u6301\u5bf9\u5176\u5916\u90e8\u4f5c\u7528\u57df\u4e2d\u53d8\u91cf\u7684\u5f15\u7528\uff0c\u5373\u4f7f\u5916\u90e8\u51fd\u6570\u5df2\u8fd4\u56de\u3002<\/li>\n\n\n\n<li><strong>\u53d8\u91cf\u63d0\u5347<\/strong>\uff1a<code>var<\/code> \u58f0\u660e\u7684\u53d8\u91cf\u4f1a\u88ab\u63d0\u5347\u5230\u4f5c\u7528\u57df\u9876\u90e8\uff0c\u4f46\u8d4b\u503c\u64cd\u4f5c\u4fdd\u6301\u539f\u4f4d\uff1b<code>let<\/code> \u548c <code>const<\/code> \u4e0d\u4f1a\u88ab\u63d0\u5347\u5230\u5df2\u521d\u59cb\u5316\u4e4b\u524d\u4f7f\u7528\u3002<\/li>\n<\/ul>\n\n\n\n<p>\u7406\u89e3\u4f5c\u7528\u57df\u5bf9\u7f16\u5199\u9ad8\u6548\u7684 JavaScript \u4ee3\u7801\u81f3\u5173\u91cd\u8981\uff0c\u5b83\u6709\u52a9\u4e8e\u907f\u514d\u547d\u540d\u51b2\u7a81\u3001\u63d0\u5347\u4ee3\u7801\u53ef\u8bfb\u6027\u548c\u53ef\u7ef4\u62a4\u6027\u3002\u66f4\u591a\u8be6\u7ec6\u5185\u5bb9\u8bf7\u5173\u6ce8\u5176\u4ed6\u76f8\u5173\u6587\u7ae0\uff01<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u5728 JavaScript \u4e2d\uff0c\u4f5c\u7528\u57df\uff08Scope\uff09 \u662f\u6307\u53d8\u91cf\u3001\u51fd\u6570\u548c\u5bf9\u8c61\u7684\u53ef\u8bbf\u95ee\u8303\u56f4\u3002\u5b83\u51b3\u5b9a\u4e86\u5982\u4f55\u67e5\u627e\u53d8\u91cf\u4ee5\u53ca [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[46],"tags":[],"class_list":["post-2025","post","type-post","status-publish","format-standard","hentry","category-javascript"],"_links":{"self":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/2025","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/comments?post=2025"}],"version-history":[{"count":1,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/2025\/revisions"}],"predecessor-version":[{"id":2026,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/2025\/revisions\/2026"}],"wp:attachment":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/media?parent=2025"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/categories?post=2025"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/tags?post=2025"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}