{"id":53597,"date":"2024-12-03T12:58:17","date_gmt":"2024-12-03T04:58:17","guid":{"rendered":"https:\/\/fwq.ai\/blog\/53597\/"},"modified":"2024-12-03T12:58:17","modified_gmt":"2024-12-03T04:58:17","slug":"javascript-%e4%b8%ad-let%e3%80%81var-%e5%92%8c-const-%e4%b9%8b%e9%97%b4%e7%9a%84%e5%8c%ba%e5%88%ab%e6%98%af%e4%bb%80%e4%b9%88%ef%bc%9a%e7%ae%80%e5%8d%95%e8%a7%a3%e9%87%8a","status":"publish","type":"post","link":"https:\/\/fwq.ai\/blog\/53597\/","title":{"rendered":"JavaScript \u4e2d let\u3001var \u548c const \u4e4b\u95f4\u7684\u533a\u522b\u662f\u4ec0\u4e48\uff1a\u7b80\u5355\u89e3\u91ca"},"content":{"rendered":"

<\/b> <\/p>\n

JavaScript \u4e2d let\u3001var \u548c const \u4e4b\u95f4\u7684\u533a\u522b\u662f\u4ec0\u4e48\uff1a\u7b80\u5355\u89e3\u91ca<\/h1>\n

<\/i>\u6536\u85cf<\/span> <\/p>\n

\u54c8\u55bd\uff01\u4eca\u5929\u5fc3\u8840\u6765\u6f6e\u7ed9\u5927\u5bb6\u5e26\u6765\u4e86\u300aJavaScript \u4e2d let\u3001var \u548c const \u4e4b\u95f4\u7684\u533a\u522b\u662f\u4ec0\u4e48\uff1a\u7b80\u5355\u89e3\u91ca\u300b<\/span>\uff0c\u60f3\u5fc5\u5927\u5bb6\u5e94\u8be5\u5bf9\u6587\u7ae0<\/span>\u90fd\u4e0d\u964c\u751f\u5427\uff0c\u90a3\u4e48\u9605\u8bfb\u672c\u6587\u5c31\u90fd\u4e0d\u4f1a\u5f88\u56f0\u96be\uff0c\u4ee5\u4e0b\u5185\u5bb9\u4e3b\u8981\u6d89\u53ca\u5230<\/span>\uff0c\u82e5\u662f\u4f60\u6b63\u5728\u5b66\u4e60\u6587\u7ae0<\/span>\uff0c\u5343\u4e07\u522b\u9519\u8fc7\u8fd9\u7bc7\u6587\u7ae0~\u5e0c\u671b\u80fd\u5e2e\u52a9\u5230\u4f60\uff01<\/p>\n

\"JavaScript<\/p>\n

\u4e86\u89e3 javascript \u4e2d let\u3001var \u548c const \u4e4b\u95f4\u7684\u533a\u522b <\/h3>\n

\u5728 javascript \u4e2d\uff0c\u60a8\u53ef\u4ee5\u4f7f\u7528 let\u3001var \u548c const \u58f0\u660e\u53d8\u91cf\u3002\u8fd9\u4e9b\u5173\u952e\u5b57\u53ef\u80fd\u770b\u8d77\u6765\u76f8\u4f3c\uff0c\u4f46\u5b83\u4eec\u5177\u6709\u5173\u952e\u5dee\u5f02\uff0c\u53ef\u4ee5\u663e\u7740\u5f71\u54cd\u4ee3\u7801\u7684\u884c\u4e3a\u65b9\u5f0f\u3002\u5728\u672c\u6587\u4e2d\uff0c\u6211\u4eec\u5c06\u89e3\u91ca\u5b83\u4eec\u4e4b\u95f4\u7684\u5dee\u5f02\uff0c\u5e76\u5e2e\u52a9\u60a8\u4e86\u89e3\u4f55\u65f6\u4f7f\u7528\u5b83\u4eec\u3002<\/p>\n

var\u3001let \u548c const \u4e4b\u95f4\u7684\u4e3b\u8981\u533a\u522b <\/h4>\n\n\n\n\n\n\n\n\n\n
var<\/strong><\/th>\n\u8ba9<\/strong><\/th>\n\u5e38\u91cf<\/strong><\/th>\n<\/tr>\n<\/thead>\n
\u5f15\u5165\u4e8e<\/strong>\uff1a\u81ea javascript \u8bde\u751f\u4ee5\u6765\u5c31\u53ef\u7528\u3002<\/td>\n \u5f15\u5165\u4e8e<\/strong>\uff1a\u6dfb\u52a0\u4e8e es6 (ecmascript 2015)\u3002<\/td>\n \u5f15\u5165\u4e8e<\/strong>\uff1a\u6dfb\u52a0\u4e8e es6 (ecmascript 2015)\u3002<\/td>\n<\/tr>\n
\u4f5c\u7528\u57df<\/strong>\uff1a\u51fd\u6570\u4f5c\u7528\u57df\u3002 var \u53d8\u91cf\u53ef\u4ee5\u5728\u58f0\u660e\u5b83\u7684\u6574\u4e2a\u51fd\u6570\u4e2d\u8bbf\u95ee\u3002<\/td>\n \u8303\u56f4<\/strong>\uff1a\u5757\u8303\u56f4\u3002 let \u53d8\u91cf\u53ea\u80fd\u5728\u58f0\u660e\u5b83\u7684\u5757 {} \u5185\u8bbf\u95ee\u3002<\/td>\n scope<\/strong>\uff1a\u5757\u4f5c\u7528\u57df\uff0c\u5c31\u50cflet\u4e00\u6837\u3002<\/td>\n<\/tr>\n
\u63d0\u5347\u884c\u4e3a<\/strong>\uff1avar \u53d8\u91cf\u88ab\u63d0\u5347\u5e76\u53ef\u4ee5\u5728\u58f0\u660e\u4e4b\u524d\u4f7f\u7528\uff08\u5c3d\u7ba1\u5b83\u4eec\u5c06\u662f\u672a\u5b9a\u4e49\u7684\uff09\u3002<\/td>\n \u63d0\u5347\u884c\u4e3a<\/strong>\uff1a\u8ba9\u53d8\u91cf\u88ab\u63d0\u5347\u4f46\u4e0d\u521d\u59cb\u5316\uff0c\u56e0\u6b64\u5728\u58f0\u660e\u4e4b\u524d\u4e0d\u80fd\u4f7f\u7528\u5b83\u4eec\u3002<\/td>\n \u63d0\u5347\u884c\u4e3a<\/strong>\uff1a\u4e0elet\u7c7b\u4f3c\uff0cconst\u53d8\u91cf\u88ab\u63d0\u5347\u4f46\u672a\u521d\u59cb\u5316\uff0c\u56e0\u6b64\u5fc5\u987b\u5728\u4f7f\u7528\u524d\u58f0\u660e\u5b83\u4eec\u3002<\/td>\n<\/tr>\n
\u91cd\u65b0\u58f0\u660e<\/strong>\uff1a\u60a8\u53ef\u4ee5\u5728\u540c\u4e00\u8303\u56f4\u5185\u91cd\u65b0\u58f0\u660e var \u53d8\u91cf\uff0c\u4e0d\u4f1a\u51fa\u73b0\u4efb\u4f55\u9519\u8bef\u3002<\/td>\n \u91cd\u65b0\u58f0\u660e<\/strong>\uff1a\u4e0d\u80fd\u5728\u540c\u4e00\u8303\u56f4\u5185\u91cd\u65b0\u58f0\u660e let \u53d8\u91cf\u3002<\/td>\n \u91cd\u65b0\u58f0\u660e<\/strong>\uff1a\u4e0d\u80fd\u91cd\u65b0\u58f0\u660e const \u53d8\u91cf\uff0c\u7c7b\u4f3c\u4e8e let\u3002<\/td>\n<\/tr>\n
\u91cd\u65b0\u8d4b\u503c<\/strong>\uff1a\u7528var\u58f0\u660e\u7684\u53d8\u91cf\u53ef\u4ee5\u88ab\u91cd\u65b0\u8d4b\u503c\u3002<\/td>\n \u91cd\u65b0\u8d4b\u503c<\/strong>\uff1a\u7528let\u58f0\u660e\u7684\u53d8\u91cf\u4e5f\u53ef\u4ee5\u91cd\u65b0\u8d4b\u503c\u3002<\/td>\n \u91cd\u65b0\u8d4b\u503c<\/strong>\uff1a\u7528const\u58f0\u660e\u7684\u53d8\u91cf\u4e0d\u80fd\u88ab\u91cd\u65b0\u8d4b\u503c\uff1b\u4ed6\u4eec\u662f\u4e0d\u53d8\u7684\u3002<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

\u4e3e\u4f8b\u8bf4\u660e\u5dee\u5f02 <\/h4>\n

\u8fd9\u662f\u4e00\u4e2a\u793a\u4f8b\uff0c\u5c55\u793a\u4e86 var\u3001let \u548c const \u7684\u4e0d\u540c\u884c\u4e3a\uff1a<\/p>\n

function userDetails(username) {\n  if (username) {\n    console.log(salary); \/\/ Output: undefined (due to hoisting)\n    console.log(age); \/\/ Error: ReferenceError: Cannot access 'age' before initialization\n    console.log(country); \/\/ Error: ReferenceError: Cannot access 'country' before initialization\n\n    let age = 30;\n    var salary = 10000;\n    const country = \"USA\";\n\n    \/\/ Trying to reassign const\n    \/\/ country = \"Canada\"; \/\/ Error: Assignment to constant variable.\n  }\n\n  console.log(salary); \/\/ Output: 10000 (accessible due to function scope)\n  console.log(age); \/\/ Error: age is not defined (due to block scope)\n  console.log(country); \/\/ Error: country is not defined (due to block scope)\n}\nuserDetails(\"John\");\n<\/pre>\n
\u793a\u4f8b\u8bf4\u660e\uff1a<\/strong><\/p>\n
    \n
  1. \n
    \u7528var\u63d0\u5347\uff1a<\/strong>\u7528var\u58f0\u660e\u7684salary\u53d8\u91cf\u88ab\u63d0\u5347\u5230\u51fd\u6570\u7684\u9876\u90e8\u3002\u8fd9\u5c31\u662f\u4e3a\u4ec0\u4e48\u4f60\u53ef\u4ee5\u5728\u58f0\u660e\u4e4b\u524d\u8bbf\u95ee\u5b83\uff0c\u5c3d\u7ba1\u5b83\u7684\u503c\u5728\u8d4b\u503c\u4e4b\u524d\u662f\u672a\u5b9a\u4e49\u7684\u3002<\/p>\n<\/li>\n
  2. \n
    \u4f7f\u7528let\u548cconst\u63d0\u5347\uff1a<\/strong>age\u548ccountry\u53d8\u91cf\u4e5f\u88ab\u63d0\u5347\uff0c\u4f46\u4e0evar\u4e0d\u540c\u7684\u662f\uff0c\u5b83\u4eec\u6ca1\u6709\u521d\u59cb\u5316\u3002\u8fd9\u610f\u5473\u7740\u60a8\u65e0\u6cd5\u5728\u58f0\u660e\u4e4b\u524d\u8bbf\u95ee\u5b83\u4eec\uff0c\u4ece\u800c\u5bfc\u81f4\u5f15\u7528\u9519\u8bef\u3002<\/p>\n<\/li>\n
  3. \n
    \u5757\u4f5c\u7528\u57df\uff1a<\/strong> \u5728 if \u5757\u4e4b\u540e\uff0c\u7531\u4e8e var \u5177\u6709\u51fd\u6570\u4f5c\u7528\u57df\uff0c\u56e0\u6b64\u4ecd\u7136\u53ef\u4ee5\u8bbf\u95ee\u5de5\u8d44\u3002\u7136\u800c\uff0cage\uff08\u7528let\u58f0\u660e\uff09\u548ccountry\uff08\u7528const\u58f0\u660e\uff09\u90fd\u662f\u5757\u4f5c\u7528\u57df\u7684\uff0c\u56e0\u6b64\u4e0d\u80fd\u5728\u5757\u5916\u8bbf\u95ee\u5b83\u4eec\u3002<\/p>\n<\/li>\n
  4. \n
    \u7528const\u91cd\u65b0\u8d4b\u503c\uff1a<\/strong>\u7528const\u58f0\u660e\u7684\u53d8\u91cf\u4e0d\u80fd\u88ab\u91cd\u65b0\u8d4b\u503c\u3002\u5728\u793a\u4f8b\u4e2d\uff0c\u5c1d\u8bd5\u66f4\u6539\u56fd\u5bb6\/\u5730\u533a\u7684\u503c\u5c06\u5bfc\u81f4\u9519\u8bef\u3002<\/p>\n<\/li>\n<\/ol>\n
     \u4f55\u65f6\u4f7f\u7528 let\u3001var \u548c const <\/h4>\n
      \n
    • \n
      \u5f53\u60a8\u9700\u8981\u4e00\u4e2a\u53ef\u4ee5\u91cd\u65b0\u5206\u914d\u4f46\u53ea\u80fd\u5728\u7279\u5b9a\u4ee3\u7801\u5757\u4e2d\u8bbf\u95ee\u7684\u53d8\u91cf\u65f6\uff0c\u8bf7\u4f7f\u7528let<\/strong>\u3002\u8fd9\u5bf9\u4e8e\u5faa\u73af\u8ba1\u6570\u5668\u3001\u6761\u4ef6\u6216\u4efb\u4f55\u5c06\u88ab\u4fee\u6539\u4f46\u4e0d\u9700\u8981\u5b58\u5728\u4e8e\u5176\u5757\u4e4b\u5916\u7684\u53d8\u91cf\u5f88\u6709\u7528\u3002<\/p>\n<\/li>\n
    • \n
      \u5728\u9700\u8981\u4e00\u4e2a\u53ef\u4ee5\u5728\u6574\u4e2a\u51fd\u6570\u4e2d\u8bbf\u95ee\u7684\u53d8\u91cf\u7684\u60c5\u51b5\u4e0b\u4f7f\u7528 var<\/strong>\uff0c\u5c3d\u7ba1\u7531\u4e8e\u5f15\u5165\u4e86 let \u548c const\uff0c\u8fd9\u5728\u73b0\u4ee3 javascript \u4e2d\u4e0d\u592a\u5e38\u89c1\u3002<\/p>\n<\/li>\n
    • \n
      \u5f53\u4f60\u60f3\u58f0\u660e\u4e00\u4e2a\u6c38\u8fdc\u4e0d\u5e94\u8be5\u91cd\u65b0\u5206\u914d\u7684\u53d8\u91cf\u65f6\uff0c\u8bf7\u4f7f\u7528 const<\/strong>\u3002\u8fd9\u5bf9\u4e8e\u5e38\u91cf\uff08\u4f8b\u5982\u914d\u7f6e\u503c\u6216\u56fa\u5b9a\u6570\u636e\uff09\u6765\u8bf4\u662f\u7406\u60f3\u7684\u9009\u62e9\uff0c\u5b83\u4eec\u5e94\u8be5\u5728\u6574\u4e2a\u4ee3\u7801\u4e2d\u4fdd\u6301\u4e0d\u53d8\u3002<\/p>\n<\/li>\n<\/ul>\n
       \u7ed3\u8bba <\/h3>\n
      \u7406\u89e3 var\u3001let \u548c const \u4e4b\u95f4\u7684\u533a\u522b\u5bf9\u4e8e\u7f16\u5199\u73b0\u4ee3\u3001\u9ad8\u6548\u7684 javascript \u81f3\u5173\u91cd\u8981\u3002\u5728\u73b0\u4ee3\u4ee3\u7801\u4e2d\uff0clet \u548c const \u901a\u5e38\u4f18\u4e8e var\uff0c\u5176\u4e2d const \u662f\u4e0d\u5e94\u91cd\u65b0\u5206\u914d\u7684\u53d8\u91cf\u7684\u9996\u9009\u3002\u901a\u8fc7\u9009\u62e9\u6b63\u786e\u7684\u5173\u952e\u5b57\uff0c\u60a8\u53ef\u4ee5\u7f16\u5199\u66f4\u6e05\u6670\u3001\u66f4\u53ef\u9760\u4e14\u4e0d\u6613\u51fa\u73b0\u9519\u8bef\u7684\u4ee3\u7801\u3002<\/p>\n
      \u901a\u8fc7\u5bf9\u4e0d\u5e94\u66f4\u6539\u7684\u503c\u4f7f\u7528 const\uff0c\u5bf9\u5757\u5185\u53ef\u80fd\u66f4\u6539\u7684\u53d8\u91cf\u4f7f\u7528 let\uff0c\u5e76\u5728\u5927\u591a\u6570\u60c5\u51b5\u4e0b\u907f\u514d\u4f7f\u7528 var\uff0c\u60a8\u7684 javascript \u4ee3\u7801\u5c06\u66f4\u5b89\u5168\u3001\u66f4\u6613\u4e8e\u7ba1\u7406\u3002<\/p>\n
      \u672c\u7bc7\u5173\u4e8e\u300aJavaScript \u4e2d let\u3001var \u548c const \u4e4b\u95f4\u7684\u533a\u522b\u662f\u4ec0\u4e48\uff1a\u7b80\u5355\u89e3\u91ca\u300b\u7684\u4ecb\u7ecd\u5c31\u5230\u6b64\u7ed3\u675f\u5566\uff0c\u4f46\u662f\u5b66\u65e0\u6b62\u5883\uff0c\u60f3\u8981\u4e86\u89e3\u5b66\u4e60\u66f4\u591a\u5173\u4e8e\u6587\u7ae0\u7684\u76f8\u5173\u77e5\u8bc6\uff0c\u8bf7\u5173\u6ce8\u7c73\u4e91\u516c\u4f17\u53f7\uff01<\/p>\n
            \u7248\u672c\u58f0\u660e \u672c\u6587\u8f6c\u8f7d\u4e8e\uff1adev.to \u5982\u6709\u4fb5\u72af\uff0c\u8bf7\u8054\u7cfb\u5220\u9664    <\/p>\n
      \n
      <\/dt>\n
      \n   \u5320\u4eba\u7f51\u6821\u7535\u8111\u7248\u600e\u4e48\u4e0b\u8f7d\uff1f\n <\/dd>\n<\/dl>\n","protected":false},"excerpt":{"rendered":"
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