{"id":341,"date":"2024-12-19T00:13:45","date_gmt":"2024-12-18T16:13:45","guid":{"rendered":"https:\/\/www.laixuexila.com\/?p=341"},"modified":"2024-12-19T00:13:45","modified_gmt":"2024-12-18T16:13:45","slug":"javascript-%e7%9a%84%e5%a3%b0%e6%98%8e%e5%8f%98%e9%87%8f%ef%bc%88let-%e5%92%8c-const%ef%bc%89","status":"publish","type":"post","link":"https:\/\/www.laixuexila.com\/index.php\/2024\/12\/19\/javascript-%e7%9a%84%e5%a3%b0%e6%98%8e%e5%8f%98%e9%87%8f%ef%bc%88let-%e5%92%8c-const%ef%bc%89\/","title":{"rendered":"JavaScript \u7684\u58f0\u660e\u53d8\u91cf\uff08let \u548c const\uff09"},"content":{"rendered":"\n
\n

\u5728 JavaScript \u4e2d\uff0c\u58f0\u660e\u53d8\u91cf\u662f\u6307\u521b\u5efa\u4e00\u4e2a\u53d8\u91cf\u5e76\u4e3a\u5176\u5206\u914d\u5185\u5b58\u7a7a\u95f4\uff0c\u4ee5\u4fbf\u5728\u7a0b\u5e8f\u4e2d\u5b58\u50a8\u6570\u636e\u3002JavaScript \u63d0\u4f9b\u4e86\u4e09\u79cd\u58f0\u660e\u53d8\u91cf\u7684\u65b9\u5f0f\uff1avar<\/code>\u3001let<\/code> \u548c const<\/code>\u3002\u5b83\u4eec\u5728\u4f5c\u7528\u57df\u3001\u63d0\u5347\u3001\u53ef\u53d8\u6027\u7b49\u65b9\u9762\u6709\u4e0d\u540c\u7684\u7279\u70b9\u3002<\/p>\n<\/blockquote>\n\n\n\n

1. var<\/code>\uff1a\u4f20\u7edf\u7684\u53d8\u91cf\u58f0\u660e\u65b9\u5f0f\uff08ES5\u53ca\u4ee5\u524d\uff0c\u4e0d\u63a8\u8350\u4f7f\u7528\uff09<\/strong><\/h3>\n\n\n\n

var<\/code> \u662f JavaScript \u4e2d\u6700\u65e9\u7684\u53d8\u91cf\u58f0\u660e\u65b9\u5f0f\u3002\u4f1a\u5b58\u5728\u4ee5\u4e0b\u95ee\u9898\uff1a<\/p>\n\n\n\n

    \n
  • var<\/code> \u4f1a\u5f15\u53d1\u4f5c\u7528\u57df\u6df7\u4e71\uff0c\u7279\u522b\u662f\u5728\u8f83\u5927\u7684\u51fd\u6570\u6216\u7a0b\u5e8f\u4e2d\uff0c\u5bb9\u6613\u5f15\u53d1\u610f\u5916\u7684\u9519\u8bef\u6216\u51b2\u7a81\u3002<\/li>\n\n\n\n
  • var<\/code> \u58f0\u660e\u7684\u53d8\u91cf\u4e0d\u5177\u5907\u5757\u7ea7\u4f5c\u7528\u57df\uff0c\u5bb9\u6613\u5bfc\u81f4\u53d8\u91cf\u6cc4\u6f0f\u5230\u5916\u90e8\u3002<\/li>\n<\/ul>\n\n\n\n

    2. let<\/code>\uff1a\u5757\u7ea7\u4f5c\u7528\u57df\u53d8\u91cf\u58f0\u660e\uff08ES6 \u5f15\u5165\uff09<\/strong><\/h3>\n\n\n\n

    let<\/code> \u662f ES6 \u5f15\u5165\u7684\u4e00\u79cd\u65b0\u7684\u58f0\u660e\u53d8\u91cf\u7684\u65b9\u5f0f\uff0c\u5b83\u63d0\u4f9b\u4e86\u5757\u7ea7\u4f5c\u7528\u57df\uff0c\u53ef\u4ee5\u6709\u6548\u907f\u514d var<\/code> \u7684\u95ee\u9898\u3002let<\/code> \u662f\u76ee\u524d\u63a8\u8350\u7684\u58f0\u660e\u53d8\u91cf\u7684\u65b9\u5f0f\u3002<\/p>\n\n\n\n

    \u7279\u70b9\uff1a<\/h4>\n\n\n\n
      \n
    • \u5757\u7ea7\u4f5c\u7528\u57df<\/strong>\uff1alet<\/code> \u58f0\u660e\u7684\u53d8\u91cf\u53ea\u5728\u5f53\u524d\u4ee3\u7801\u5757\uff08\u7531 {}<\/code> \u5305\u56f4\u7684\u533a\u57df\uff09\u5185\u6709\u6548\u3002\u4f8b\u5982\uff0c\u5728\u4e00\u4e2a for<\/code> \u5faa\u73af\u6216\u8005 if<\/code> \u5757\u5185\u58f0\u660e\u7684\u53d8\u91cf\uff0c\u4ec5\u5728\u8be5\u5757\u5185\u6709\u6548\u3002<\/li>\n\n\n\n
    • \u4e0d\u63d0\u5347\u5230\u9876\u90e8<\/strong>\uff1alet<\/code> \u4e0d\u4f1a\u5c06\u53d8\u91cf\u63d0\u5347\u5230\u4f5c\u7528\u57df\u7684\u9876\u90e8\u3002\u5c1d\u8bd5\u5728\u58f0\u660e\u4e4b\u524d\u4f7f\u7528 let<\/code> \u58f0\u660e\u7684\u53d8\u91cf\uff0c\u4f1a\u629b\u51fa ReferenceError<\/code> \u9519\u8bef\u3002<\/li>\n\n\n\n
    • \u53ef\u4ee5\u91cd\u65b0\u8d4b\u503c<\/strong>\uff1a\u4e0e var<\/code> \u4e00\u6837\uff0clet<\/code> \u58f0\u660e\u7684\u53d8\u91cf\u53ef\u4ee5\u91cd\u65b0\u8d4b\u503c\u3002<\/li>\n<\/ul>\n\n\n\n

      \u793a\u4f8b\uff1a<\/h4>\n\n\n\n
      let x = 5;\nif (true) {\n    let x = 10;  \/\/ \u5757\u7ea7\u4f5c\u7528\u57df\u5185\u7684 x\n    console.log(x);  \/\/ \u8f93\u51fa 10\n}\nconsole.log(x);  \/\/ \u8f93\u51fa 5\uff0c\u5916\u90e8 x \u7684\u503c\u6ca1\u6709\u6539\u53d8<\/code><\/pre>\n\n\n\n
      let y = 10;\ny = 20;  \/\/ \u91cd\u65b0\u8d4b\u503c\u662f\u5141\u8bb8\u7684\nconsole.log(y);  \/\/ \u8f93\u51fa 20<\/code><\/pre>\n\n\n\n
      let<\/code> \u7684\u63d0\u5347\uff1a<\/h4>\n\n\n\n
      console.log(a); \/\/ ReferenceError: Cannot access 'a' before initialization\nlet a = 5;<\/code><\/pre>\n\n\n\n
      \u5728\u6b64\u793a\u4f8b\u4e2d\uff0clet<\/code> \u58f0\u660e\u7684\u53d8\u91cf\u4e0d\u4f1a\u88ab\u63d0\u5347\uff0ca<\/code> \u5fc5\u987b\u5728\u58f0\u660e\u4e4b\u540e\u624d\u80fd\u4f7f\u7528\u3002<\/p>\n\n\n\n
      3. const<\/code>\uff1a\u5e38\u91cf\u58f0\u660e\uff08ES6 \u5f15\u5165\uff09<\/strong><\/h3>\n\n\n\n
      const<\/code> \u4e5f\u662f ES6 \u5f15\u5165\u7684\u4e00\u79cd\u58f0\u660e\u53d8\u91cf\u7684\u65b9\u5f0f\uff0c\u7528\u4e8e\u58f0\u660e\u5e38\u91cf\u3002\u5e38\u91cf\u4e00\u65e6\u88ab\u8d4b\u503c\uff0c\u4e0d\u80fd\u518d\u91cd\u65b0\u8d4b\u503c\u3002<\/p>\n\n\n\n
      \u7279\u70b9\uff1a<\/h4>\n\n\n\n
        \n
      • \u5757\u7ea7\u4f5c\u7528\u57df<\/strong>\uff1a\u4e0e let<\/code> \u76f8\u540c\uff0cconst<\/code> \u4e5f\u5177\u6709\u5757\u7ea7\u4f5c\u7528\u57df\u3002<\/li>\n\n\n\n
      • \u5e38\u91cf<\/strong>\uff1aconst<\/code> \u58f0\u660e\u7684\u53d8\u91cf\u662f\u5e38\u91cf\uff0c\u8d4b\u503c\u540e\u65e0\u6cd5\u518d\u4fee\u6539\u3002<\/li>\n\n\n\n
      • \u5fc5\u987b\u521d\u59cb\u5316<\/strong>\uff1aconst<\/code> \u58f0\u660e\u65f6\uff0c\u5fc5\u987b\u7acb\u5373\u521d\u59cb\u5316\uff0c\u5426\u5219\u4f1a\u629b\u51fa\u8bed\u6cd5\u9519\u8bef\u3002<\/li>\n<\/ul>\n\n\n\n
        \u793a\u4f8b\uff1a<\/h4>\n\n\n\n
        const pi = 3.14159;\nconsole.log(pi);  \/\/ \u8f93\u51fa 3.14159\n\n\/\/ \u5c1d\u8bd5\u91cd\u65b0\u8d4b\u503c\u4f1a\u629b\u51fa\u9519\u8bef\npi = 3.14;  \/\/ TypeError: Assignment to constant variable.<\/code><\/pre>\n\n\n\n
        \u5bf9\u8c61\u548c\u6570\u7ec4\u7684\u5e38\u91cf\uff1a<\/h4>\n\n\n\n
        const<\/code> \u58f0\u660e\u7684\u5e38\u91cf\u53ef\u4ee5\u6307\u5411\u5bf9\u8c61\u6216\u6570\u7ec4\uff0c\u4f46\u4e0d\u80fd\u91cd\u65b0\u8d4b\u503c\u6574\u4e2a\u5bf9\u8c61\u6216\u6570\u7ec4\u3002\u5982\u679c\u662f\u5bf9\u8c61\u6216\u6570\u7ec4\uff0c\u5219\u53ef\u4ee5\u4fee\u6539\u5bf9\u8c61\u7684\u5c5e\u6027\u6216\u6570\u7ec4\u7684\u5143\u7d20\u3002<\/p>\n\n\n\n
        const person = { name: \"John\", age: 30 };\nperson.age = 31;  \/\/ \u8fd9\u662f\u5408\u6cd5\u7684\uff0c\u4fee\u6539\u5bf9\u8c61\u5c5e\u6027\nconsole.log(person.age);  \/\/ \u8f93\u51fa 31\n\n\/\/ \u4f46\u4e0d\u80fd\u91cd\u65b0\u8d4b\u503c\u6574\u4e2a\u5bf9\u8c61\nperson = { name: \"Jane\", age: 25 };  \/\/ TypeError: Assignment to constant variable.<\/code><\/pre>\n\n\n\n
        const arr = [1, 2, 3];\narr.push(4);  \/\/ \u53ef\u4ee5\u4fee\u6539\u6570\u7ec4\nconsole.log(arr);  \/\/ \u8f93\u51fa [1, 2, 3, 4]\n\n\/\/ \u4f46\u4e0d\u80fd\u91cd\u65b0\u8d4b\u503c\u6574\u4e2a\u6570\u7ec4\narr = [1, 2, 3, 4];  \/\/ TypeError: Assignment to constant variable.<\/code><\/pre>\n\n\n\n
        4. var<\/code>\u3001let<\/code> \u548c const<\/code> \u7684\u5bf9\u6bd4<\/strong><\/h3>\n\n\n\n
        \u7279\u6027<\/th>var<\/code><\/th>let<\/code><\/th>const<\/code><\/th><\/tr><\/thead>
        \u4f5c\u7528\u57df<\/strong><\/td>\u51fd\u6570\u4f5c\u7528\u57df \/ \u5168\u5c40\u4f5c\u7528\u57df<\/td>\u5757\u7ea7\u4f5c\u7528\u57df<\/td>\u5757\u7ea7\u4f5c\u7528\u57df<\/td><\/tr>
        \u63d0\u5347\uff08Hoisting\uff09<\/strong><\/td>\u4f1a\u63d0\u5347\uff08\u58f0\u660e\u63d0\u5347\uff0c\u4f46\u8d4b\u503c\u4e0d\u4f1a\u63d0\u5347\uff09<\/td>\u4e0d\u4f1a\u63d0\u5347\uff0c\u5fc5\u987b\u5148\u58f0\u660e\u518d\u4f7f\u7528<\/td>\u4e0d\u4f1a\u63d0\u5347\uff0c\u5fc5\u987b\u5148\u58f0\u660e\u518d\u4f7f\u7528<\/td><\/tr>
        \u91cd\u65b0\u8d4b\u503c<\/strong><\/td>\u53ef\u4ee5\u91cd\u65b0\u8d4b\u503c<\/td>\u53ef\u4ee5\u91cd\u65b0\u8d4b\u503c<\/td>\u4e0d\u80fd\u91cd\u65b0\u8d4b\u503c<\/td><\/tr>
        \u662f\u5426\u5fc5\u987b\u521d\u59cb\u5316<\/strong><\/td>\u4e0d\u5fc5\u987b\u521d\u59cb\u5316<\/td>\u4e0d\u5fc5\u987b\u521d\u59cb\u5316<\/td>\u5fc5\u987b\u521d\u59cb\u5316<\/td><\/tr>
        \u5bf9\u8c61\/\u6570\u7ec4\u7684\u53ef\u4fee\u6539\u6027<\/strong><\/td>\u53ef\u4ee5\u4fee\u6539\u5bf9\u8c61\u6216\u6570\u7ec4\u7684\u5185\u5bb9<\/td>\u53ef\u4ee5\u4fee\u6539\u5bf9\u8c61\u6216\u6570\u7ec4\u7684\u5185\u5bb9<\/td>\u4e0d\u80fd\u91cd\u65b0\u8d4b\u503c\u6574\u4e2a\u5bf9\u8c61\u6216\u6570\u7ec4<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
        5. \u603b\u7ed3<\/strong><\/h3>\n\n\n\n
          \n
        • \u4f7f\u7528 var<\/code> \u58f0\u660e\u7684\u53d8\u91cf\u5177\u6709\u51fd\u6570\u4f5c\u7528\u57df\uff0c\u4e14\u652f\u6301\u63d0\u5347\uff0c\u4f46\u5bb9\u6613\u5bfc\u81f4\u4f5c\u7528\u57df\u95ee\u9898\uff0c\u4e0d\u63a8\u8350\u5728\u73b0\u4ee3 JavaScript \u4e2d\u4f7f\u7528\u3002<\/li>\n\n\n\n
        • \u4f7f\u7528 let<\/code> \u58f0\u660e\u7684\u53d8\u91cf\u5177\u6709\u5757\u7ea7\u4f5c\u7528\u57df\uff0c\u4e14\u4e0d\u4f1a\u63d0\u5347\uff0c\u63a8\u8350\u7528\u4e8e\u5927\u591a\u6570\u573a\u666f\u3002<\/li>\n\n\n\n
        • \u4f7f\u7528 const<\/code> \u58f0\u660e\u5e38\u91cf\uff0c\u8d4b\u503c\u540e\u4e0d\u80fd\u4fee\u6539\uff0c\u5e38\u7528\u4e8e\u4e0d\u5e0c\u671b\u4fee\u6539\u7684\u503c\uff08\u5982\u5e38\u91cf\u3001\u5f15\u7528\u7c7b\u578b\u7684\u5c5e\u6027\u7b49\uff09\u3002<\/li>\n<\/ul>\n\n\n\n
          \u901a\u5e38\u60c5\u51b5\u4e0b\uff0c\u63a8\u8350\u4f18\u5148\u4f7f\u7528 let<\/code> \u548c const<\/code>\uff0c\u800c\u907f\u514d\u4f7f\u7528 var<\/code>\uff0c\u4ee5\u63d0\u9ad8\u4ee3\u7801\u7684\u53ef\u7ef4\u62a4\u6027\u548c\u907f\u514d\u4e00\u4e9b\u6f5c\u5728\u7684\u9519\u8bef\u3002\u66f4\u591a\u8be6\u7ec6\u5185\u5bb9\u8bf7\u5173\u6ce8\u5176\u4ed6\u76f8\u5173\u6587\u7ae0\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"
          \u5728 JavaScript \u4e2d\uff0c\u58f0\u660e\u53d8\u91cf\u662f\u6307\u521b\u5efa\u4e00\u4e2a\u53d8\u91cf\u5e76\u4e3a\u5176\u5206\u914d\u5185\u5b58\u7a7a\u95f4\uff0c\u4ee5\u4fbf\u5728\u7a0b\u5e8f\u4e2d\u5b58\u50a8\u6570\u636e\u3002JavaScr […]<\/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-341","post","type-post","status-publish","format-standard","hentry","category-javascript"],"_links":{"self":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/341","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=341"}],"version-history":[{"count":1,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/341\/revisions"}],"predecessor-version":[{"id":342,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/341\/revisions\/342"}],"wp:attachment":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/media?parent=341"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/categories?post=341"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/tags?post=341"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}