{"id":158700,"date":"2024-05-08T12:55:52","date_gmt":"2024-05-08T04:55:52","guid":{"rendered":"https:\/\/docs.pingcode.com\/ask\/ask-ask\/158700.html"},"modified":"2024-05-08T12:55:55","modified_gmt":"2024-05-08T04:55:55","slug":"%e5%a6%82%e4%bd%95%e7%90%86%e8%a7%a3-javascript-%e4%b8%ad-var-%e5%92%8c-let-%e7%9a%84%e5%8c%ba%e5%88%ab","status":"publish","type":"post","link":"https:\/\/docs.pingcode.com\/ask\/ask-ask\/158700.html","title":{"rendered":"\u5982\u4f55\u7406\u89e3 JavaScript \u4e2d var \u548c let \u7684\u533a\u522b"},"content":{"rendered":"

\"\u5982\u4f55\u7406\u89e3<\/p>\n

\u5728JavaScript\u4e2d\uff0c\u7406\u89e3var<\/code>\u548clet<\/code>\u7684\u533a\u522b\u5bf9\u4e8e\u7f16\u5199\u9ad8\u6548\u3001\u53ef\u9760\u7684\u4ee3\u7801\u81f3\u5173\u91cd\u8981\u3002\u9996\u8981\u7684\u533a\u522b\u5728\u4e8e\u5b83\u4eec\u7684\u4f5c\u7528\u57df\u3001\u63d0\u5347\uff08hoisting\uff09\u884c\u4e3a\u548c\u91cd\u590d\u58f0\u660e\u7684\u5141\u8bb8\u7a0b\u5ea6\u3002\u5177\u4f53\u800c\u8a00\uff0cvar<\/code>\u58f0\u660e\u7684\u53d8\u91cf\u62e5\u6709\u51fd\u6570\u4f5c\u7528\u57df\u6216\u5168\u5c40\u4f5c\u7528\u57df\uff0c\u800c\u4e0d\u662f\u5757\u4f5c\u7528\u57df\uff0c\u8fd9\u610f\u5473\u7740\u5b83\u4eec\u53ef\u4ee5\u5728\u58f0\u660e\u6240\u5728\u7684\u6574\u4e2a\u51fd\u6570\u6216\u5168\u5c40\u4e0a\u4e0b\u6587\u4e2d\u88ab\u8bbf\u95ee\u548c\u4fee\u6539\u3002\u800clet<\/code>\u58f0\u660e\u7684\u53d8\u91cf\u5219\u5177\u6709\u5757\u7ea7\u4f5c\u7528\u57df\uff0c\u53ea\u80fd\u5728\u5176\u58f0\u660e\u7684\u4ee3\u7801\u5757\u91cc\u88ab\u8bbf\u95ee\u3002\u8fd9\u4e2a\u660e\u663e\u7684\u4f5c\u7528\u57df\u5dee\u5f02\u5e26\u6765\u4e86\u66f4\u597d\u7684\u4ee3\u7801\u6a21\u5757\u5316\u548c\u964d\u4f4e\u4e86\u53d8\u91cf\u51b2\u7a81\u7684\u98ce\u9669\u3002<\/p>\n<\/p>\n

\u63a5\u4e0b\u6765\u6211\u4eec\u5c06\u8be6\u7ec6\u63a2\u8ba8\u5176\u4e2d\u4e00\u70b9\uff1a\u5757\u7ea7\u4f5c\u7528\u57df\u5bf9JavaScript\u7f16\u7a0b\u7684\u5f71\u54cd<\/strong>\u3002\u4e0evar<\/code>\u76f8\u6bd4\uff0clet<\/code>\u5141\u8bb8\u5f00\u53d1\u8005\u66f4\u7ec6\u7c92\u5ea6\u5730\u63a7\u5236\u53d8\u91cf\u7684\u53ef\u8bbf\u95ee\u6027\u3002\u4f8b\u5982\uff0c\u5728\u4e00\u4e2a\u5faa\u73af\u4e2d\u4f7f\u7528let<\/code>\u58f0\u660e\u7684\u53d8\u91cf\u5c06\u786e\u4fdd\u8be5\u53d8\u91cf\u4ec5\u5728\u5faa\u73af\u4f53\u5185\u90e8\u88ab\u8bbf\u95ee\u548c\u4fee\u6539\uff0c\u8fd9\u964d\u4f4e\u4e86\u53d8\u91cf\u610f\u5916\u5e72\u6270\u5faa\u73af\u903b\u8f91\u4e4b\u5916\u7684\u4ee3\u7801\u7684\u98ce\u9669\u3002\u8fd9\u79cd\u4f5c\u7528\u57df\u9650\u5236\u589e\u52a0\u4e86\u4ee3\u7801\u7684\u53ef\u8bfb\u6027\u548c\u53ef\u7ef4\u62a4\u6027\uff0c\u4f7f\u5f97\u53d8\u91cf\u7684\u7ba1\u7406\u66f4\u52a0\u76f4\u89c2\u3002<\/p>\n<\/p>\n

\u4e00\u3001\u4f5c\u7528\u57df\u5dee\u5f02<\/h3>\n<\/p>\n

\u5728JavaScript\u4e2d\u7406\u89e3\u53d8\u91cf\u7684\u4f5c\u7528\u57df\u662f\u81f3\u5173\u91cd\u8981\u7684\uff0c\u56e0\u4e3a\u5b83\u51b3\u5b9a\u4e86\u4ee3\u7801\u7684\u6267\u884c\u65b9\u5f0f\u548c\u53d8\u91cf\u7684\u53ef\u89c1\u6027\u3002var<\/code>\u548clet<\/code>\u4e4b\u95f4\u7684\u4f5c\u7528\u57df\u5dee\u5f02\u662f\u5b83\u4eec\u7684\u4e3b\u8981\u533a\u522b\u4e4b\u4e00\u3002<\/p>\n<\/p>\n

var<\/code>\u7684\u51fd\u6570\u7ea7\u4f5c\u7528\u57df\u610f\u5473\u7740<\/strong>\uff0c\u5f53var<\/code>\u53d8\u91cf\u5728\u51fd\u6570\u5185\u90e8\u58f0\u660e\u65f6\uff0c\u5b83\u5728\u6574\u4e2a\u51fd\u6570\u4e2d\u90fd\u662f\u53ef\u8bbf\u95ee\u7684\uff0c\u5373\u4fbf\u662f\u5728\u58f0\u660e\u4e4b\u524d\u3002\u8fd9\u662f\u56e0\u4e3aJavaScript\u7684\u63d0\u5347\u673a\u5236\uff0c\u5176\u4e2dvar<\/code>\u58f0\u660e\u7684\u53d8\u91cf\u4f1a\u88ab\u63d0\u5347\u5230\u51fd\u6570\u7684\u9876\u90e8\u3002\u800c\u5728\u51fd\u6570\u5916\u90e8\u58f0\u660e\u7684var<\/code>\u53d8\u91cf\u6210\u4e3a\u5168\u5c40\u53d8\u91cf\uff0c\u53ef\u5728\u6574\u4e2a\u7a0b\u5e8f\u4e2d\u8bbf\u95ee\u3002<\/p>\n<\/p>\n

let<\/code>\u7684\u5757\u7ea7\u4f5c\u7528\u57df<\/strong>\uff0c\u5219\u66f4\u52a0\u4e25\u683c\u3002\u5b83\u786e\u4fdd\u53d8\u91cf\u4ec5\u5728\u58f0\u660e\u5b83\u7684\u4ee3\u7801\u5757\uff08\u4f8b\u5982\uff1a\u5faa\u73af\u3001if\u6761\u4ef6\u53e5\u7b49\uff09\u5185\u90e8\u53ef\u89c1\u3002\u8fd9\u5bf9\u4e8e\u907f\u514d\u5728\u590d\u6742\u51fd\u6570\u6216\u5e94\u7528\u4e2d\u7684\u53d8\u91cf\u51b2\u7a81\u548c\u610f\u5916\u4fee\u6539\u975e\u5e38\u6709\u7528\u3002<\/p>\n<\/p>\n

\u4e8c\u3001\u63d0\u5347\u884c\u4e3a<\/h3>\n<\/p>\n

\u63d0\u5347\uff08hoisting\uff09\u662fJavaScript\u4e2d\u4e00\u4e2a\u91cd\u8981\u4e14\u6709\u65f6\u4ee4\u4eba\u56f0\u60d1\u7684\u6982\u5ff5\u3002\u5b83\u6307\u7684\u662f\u53d8\u91cf\u548c\u51fd\u6570\u58f0\u660e\u5728\u4ee3\u7801\u6267\u884c\u524d\u88ab\u79fb\u81f3\u5176\u4f5c\u7528\u57df\u9876\u90e8\u7684\u73b0\u8c61\u3002<\/p>\n<\/p>\n

var<\/code>\u58f0\u660e\u7684\u53d8\u91cf\u88ab\u63d0\u5347<\/strong>\uff0c\u4f46\u662f\u53ea\u63d0\u5347\u4e86\u58f0\u660e\uff0c\u800c\u4e0d\u5305\u62ec\u521d\u59cb\u5316\u3002\u8fd9\u610f\u5473\u7740\u5728\u58f0\u660e\u4e4b\u524d\u8bbf\u95eevar<\/code>\u53d8\u91cf\u4e0d\u4f1a\u62a5\u9519\uff0c\u800c\u662f\u4f1a\u5f97\u5230undefined<\/code>\u503c\u3002<\/p>\n<\/p>\n

\u76f8\u53cd\uff0clet<\/code>\u58f0\u660e\u7684\u53d8\u91cf\u4e5f\u63d0\u5347\u4e86<\/strong>\uff0c\u4f46\u662fJavaScript\u521b\u5efa\u4e86\u4e00\u4e2a\u201c\u6682\u65f6\u6027\u6b7b\u533a\u201d\uff08Temporal Dead Zone\uff09\uff0c\u76f4\u5230\u53d8\u91cf\u7684\u58f0\u660e\u88ab\u6267\u884c\u3002\u5728\u8fd9\u4e2a\u9636\u6bb5\u91cc\u8bbf\u95ee\u53d8\u91cf\u4f1a\u5bfc\u81f4\u53c2\u8003\u9519\u8bef\uff08Reference Error\uff09\uff0c\u8fd9\u5f3a\u5236\u5f00\u53d1\u8005\u5199\u51fa\u66f4\u52a0\u89c4\u8303\u548c\u53ef\u9884\u6d4b\u7684\u4ee3\u7801\u3002<\/p>\n<\/p>\n

\u4e09\u3001\u91cd\u590d\u58f0\u660e\u7684\u5141\u8bb8<\/h3>\n<\/p>\n

\u5728\u4e00\u4e2a\u4f5c\u7528\u57df\u5185\u91cd\u590d\u58f0\u660e\u540c\u4e00\u4e2a\u53d8\u91cf\u5728\u7f16\u7a0b\u4e2d\u5e38\u5e38\u662f\u4e0d\u53ef\u53d6\u7684\uff0c\u56e0\u4e3a\u5b83\u53ef\u80fd\u5bfc\u81f4\u4ee3\u7801\u903b\u8f91\u6df7\u4e71\u548c\u96be\u4ee5\u8ddf\u8e2a\u7684\u9519\u8bef\u3002<\/p>\n<\/p>\n

var<\/code>\u5141\u8bb8\u5728\u540c\u4e00\u4e2a\u4f5c\u7528\u57df\u5185\u91cd\u590d\u58f0\u660e\u53d8\u91cf<\/strong>\uff0c\u8fd9\u589e\u52a0\u4e86\u4ee3\u7801\u51fa\u9519\u7684\u51e0\u7387\u3002\u5982\u679c\u4e0d\u5c0f\u5fc3\u91cd\u590d\u58f0\u660e\uff0c\u65b0\u7684\u58f0\u660e\u4f1a\u8986\u76d6\u524d\u9762\u7684\u58f0\u660e\uff0c\u800c\u4e0d\u4f1a\u629b\u51fa\u4efb\u4f55\u9519\u8bef\u3002<\/p>\n<\/p>\n

\u7136\u800c\uff0clet<\/code>\u5219\u4e0d\u5141\u8bb8\u5728\u76f8\u540c\u4f5c\u7528\u57df\u5185\u91cd\u590d\u58f0\u660e\u540c\u4e00\u4e2a\u540d\u5b57\u7684\u53d8\u91cf<\/strong>\u3002\u5c1d\u8bd5\u8fd9\u6837\u505a\u5c06\u4f1a\u5bfc\u81f4\u8bed\u6cd5\u9519\u8bef\uff0c\u4ece\u800c\u5f3a\u5236\u5f00\u53d1\u8005\u5728\u7f16\u7801\u8fc7\u7a0b\u4e2d\u907f\u514d\u4f7f\u7528\u540c\u4e00\u4e2a\u540d\u5b57\u6807\u8bc6\u4e0d\u540c\u7684\u53d8\u91cf\uff0c\u51cf\u5c11\u4e86\u6f5c\u5728\u7684bug\u6765\u6e90\u3002<\/p>\n<\/p>\n

\u56db\u3001\u6700\u4f73\u5b9e\u8df5<\/h3>\n<\/p>\n

\u867d\u7136var<\/code>\u5728\u8fc7\u53bb\u7684JavaScript\u7248\u672c\u4e2d\u5341\u5206\u5e38\u7528\uff0c\u4f46\u73b0\u4ee3JavaScript\uff08ES6\u53ca\u4ee5\u540e\u7248\u672c\uff09\u63a8\u8350\u4f7f\u7528let<\/code>\u548cconst<\/code>\u6765\u58f0\u660e\u53d8\u91cf\uff0c\u4e3b\u8981\u662f\u56e0\u4e3a\u5b83\u4eec\u63d0\u4f9b\u4e86\u66f4\u6e05\u6670\u7684\u4f5c\u7528\u57df\u7ba1\u7406\u3001\u51cf\u5c11\u4e86\u63d0\u5347\u5e26\u6765\u7684\u6df7\u4e71\u3001\u4ee5\u53ca\u9632\u6b62\u53d8\u91cf\u88ab\u610f\u5916\u91cd\u590d\u58f0\u660e\u3002<\/p>\n<\/p>\n

\u5728\u5b9e\u9645\u5f00\u53d1\u4e2d\uff0c\u63a8\u8350\u4f7f\u7528let<\/code>\u8fdb\u884c\u5c40\u90e8\u53d8\u91cf\u7684\u58f0\u660e<\/strong>\uff0c\u8fd9\u6837\u53ef\u4ee5\u786e\u4fdd\u53d8\u91cf\u53ea\u5728\u6240\u9700\u7684\u4ee3\u7801\u5757\u5185\u53ef\u89c1\uff0c\u5e76\u4e14\u51cf\u5c11\u5168\u5c40\u53d8\u91cf\u7684\u4f7f\u7528\uff0c\u964d\u4f4e\u53d8\u91cf\u51b2\u7a81\u7684\u53ef\u80fd\u6027\u3002\u5f53\u53d8\u91cf\u503c\u9700\u8981\u5728\u7a0b\u5e8f\u6267\u884c\u8fc7\u7a0b\u4e2d\u6539\u53d8\u65f6\uff0clet<\/code>\u662f\u5408\u9002\u7684\u9009\u62e9\u3002\u53cd\u4e4b\uff0c\u5982\u679c\u4e00\u4e2a\u53d8\u91cf\u5728\u6574\u4e2a\u751f\u547d\u5468\u671f\u5185\u4e0d\u9700\u8981\u6539\u53d8\uff0c\u5e94\u8be5\u4f7f\u7528const<\/code>\u6765\u58f0\u660e\uff0c\u8fd9\u6837\u4e0d\u4ec5\u53ef\u4ee5\u63d0\u5347\u4ee3\u7801\u7684\u53ef\u8bfb\u6027\uff0c\u8fd8\u53ef\u4ee5\u5229\u7528JavaScript\u5f15\u64ce\u5bf9\u5e38\u91cf\u7684\u4f18\u5316\u3002<\/p>\n<\/p>\n

\u7ed3\u8bba\uff1a\u7406\u89e3var<\/code>\u548clet<\/code>\u7684\u533a\u522b\uff0c\u5e76\u6070\u5f53\u5730\u4f7f\u7528\u5b83\u4eec\uff0c\u5bf9\u4e8e\u7f16\u5199\u6e05\u6670\u3001\u9ad8\u6548\u3001\u53ef\u7ef4\u62a4\u7684JavaScript\u4ee3\u7801\u975e\u5e38\u5173\u952e\u3002\u968f\u7740JavaScript\u8bed\u8a00\u7684\u53d1\u5c55\uff0c\u4f7f\u7528let<\/code>\u548cconst<\/code>\u5c06\u6210\u4e3a\u66f4\u52a0\u666e\u904d\u548c\u63a8\u8350\u7684\u5b9e\u8df5\u3002<\/p>\n<\/p>\n

\u76f8\u5173\u95ee\u7b54FAQs\uff1a<\/strong><\/h2>\n
    \n
  1. \n

    \u5728 JavaScript \u4e2d\uff0cvar \u548c let \u6709\u4ec0\u4e48\u4e0d\u540c\u4e4b\u5904\uff1f<\/strong>
    \n\u5f53\u6211\u4eec\u5728 JavaScript \u4e2d\u58f0\u660e\u53d8\u91cf\u65f6\uff0c\u6211\u4eec\u901a\u5e38\u53ef\u4ee5\u4f7f\u7528var\u6216let\u5173\u952e\u5b57\u3002\u8fd9\u4e24\u4e2a\u5173\u952e\u5b57\u4e4b\u95f4\u6709\u4e00\u4e9b\u91cd\u8981\u7684\u533a\u522b\u3002\u9996\u5148\uff0cvar\u88ab\u8ba4\u4e3a\u662f\u51fd\u6570\u4f5c\u7528\u57df\u7684\uff0c\u800clet\u662f\u5757\u7ea7\u4f5c\u7528\u57df\u7684\u3002\u8fd9\u610f\u5473\u7740\u4f7f\u7528var\u58f0\u660e\u7684\u53d8\u91cf\u53ea\u5728\u51fd\u6570\u5185\u90e8\u662f\u53ef\u89c1\u7684\uff0c\u800c\u4f7f\u7528let\u58f0\u660e\u7684\u53d8\u91cf\u5219\u5728\u5305\u542b\u5176\u7684\u4ee3\u7801\u5757\u5185\u90e8\u53ef\u89c1\u3002<\/p>\n<\/li>\n

  2. \n

    \u4e3a\u4ec0\u4e48\u5e94\u8be5\u4f7f\u7528let\u800c\u4e0d\u662fvar\u6765\u58f0\u660e\u53d8\u91cf\uff1f<\/strong>
    \n\u4f7f\u7528let\u800c\u4e0d\u662fvar\u53ef\u4ee5\u907f\u514d\u53d8\u91cf\u63d0\u5347\u5e26\u6765\u7684\u56f0\u60d1\u548c\u4e0d\u53ef\u9884\u6d4b\u6027\u3002\u53d8\u91cf\u63d0\u5347\u662f\u6307\u5728\u4ee3\u7801\u6267\u884c\u4e4b\u524d\uff0c\u53d8\u91cf\u58f0\u660e\u88ab\u63d0\u5347\u81f3\u5176\u4f5c\u7528\u57df\u9876\u90e8\u7684\u73b0\u8c61\u3002\u8fd9\u610f\u5473\u7740\u4f7f\u7528var\u58f0\u660e\u7684\u53d8\u91cf\u53ef\u4ee5\u5728\u5176\u5b9e\u9645\u58f0\u660e\u4e4b\u524d\u88ab\u8bbf\u95ee\u548c\u4f7f\u7528\uff0c\u8fd9\u53ef\u80fd\u5bfc\u81f4\u4ee3\u7801\u903b\u8f91\u4e0a\u7684\u9519\u8bef\u3002\u4f7f\u7528let\u58f0\u660e\u53d8\u91cf\u53ef\u4ee5\u89e3\u51b3\u8fd9\u4e2a\u95ee\u9898\uff0c\u56e0\u4e3a\u53d8\u91cf\u53ea\u6709\u5728\u5176\u5b9e\u9645\u58f0\u660e\u4e4b\u540e\u624d\u53ef\u4ee5\u88ab\u8bbf\u95ee\u3002<\/p>\n<\/li>\n

  3. \n

    \u5728\u4ec0\u4e48\u60c5\u51b5\u4e0b\u5e94\u8be5\u4f7f\u7528var\u800c\u4e0d\u662flet\uff1f<\/strong>
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