{"id":574,"date":"2025-07-29T23:04:21","date_gmt":"2025-07-29T15:04:21","guid":{"rendered":"https:\/\/spc.huaweitianli.com\/?p=574"},"modified":"2025-07-29T23:05:55","modified_gmt":"2025-07-29T15:05:55","slug":"var-let-const","status":"publish","type":"post","link":"https:\/\/www.sunpengcheng.com\/index.php\/2025\/07\/29\/var-let-const\/","title":{"rendered":"\u5f7b\u5e95\u5f04\u6e05\u695avar let const\u7684\u533a\u522b"},"content":{"rendered":"<p>\u4eca\u5929\u53c8\u6709\u5c0f\u4f19\u4f34\u95ee\u6211\u4e00\u4e2a\u8fd9\u6837\u7684\u95ee\u9898\uff0cJavaScript\u4e2d\uff0c\u4e3a\u4ec0\u4e48\u6709\u7684\u53d8\u91cf\u7528var\u5b9a\u4e49\uff0c\u6709\u7684\u7528let\uff0c\u8fd8\u6709\u7684\u7528const\u5462\uff1f<\/p>\n<p>\u5148\u7ed9\u51fa\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<h3>\u5e38\u7528\u573a\u666f<\/h3>\n<ul>\n<li>const \u4f18\u5148\u4f7f\u7528\uff0c\u5c24\u5176\u662f\u5e38\u91cf\u3001\u5bf9\u8c61\u3001\u6570\u7ec4\uff0c\uff08\u5360 80% \u573a\u666f\uff09<\/li>\n<li>let \u9700\u8981\u4fee\u6539\u65f6\u4f7f\u7528\uff0c\u9700\u8981\u91cd\u65b0\u8d4b\u503c\u7684\u53d8\u91cf\uff08\u5982\u5faa\u73af\u3001\u6761\u4ef6\u5206\u652f\uff09\uff0c\uff08\u5360 20% \u573a\u666f\uff09<\/li>\n<li>var \u6c38\u8fdc\u4e0d\u7528<\/li>\n<\/ul>\n<h3>\u9996\u5148\u662f\u4f5c\u7528\u57df\u4e0d\u4e00\u6837<\/h3>\n<ul>\n<li>var\u58f0\u660e\u7684\u53d8\u91cf\u662f\u5168\u5c40\u4f5c\u7528\u57df\u6216\u51fd\u6570\u4f5c\u7528\u57df<\/li>\n<li>let\u548cconst\u58f0\u660e\u7684\u53d8\u91cf\u662f\u5757\u7ea7\u4f5c\u7528\u57df<\/li>\n<\/ul>\n<h3>\u91cd\u65b0\u58f0\u660e &amp; \u503c\u66f4\u65b0<\/h3>\n<ul>\n<li>var\u58f0\u660e\u7684\u53d8\u91cf\uff0c\u53ef\u4ee5\u91cd\u65b0\u58f0\u660e\uff0c\u4e5f\u53ef\u4ee5\u8fdb\u884c\u66f4\u65b0\uff1b<\/li>\n<li>let\u58f0\u660e\u7684\u53d8\u91cf\uff0c\u4e0d\u53ef\u4ee5\u518d\u58f0\u660e\uff0c\u4f46\u53ef\u4ee5\u8fdb\u884c\u66f4\u65b0\uff1b\n<ul>\n<li>\u91cd\u65b0\u58f0\u660e\u4f1a\u62a5\u9519 <code>Uncaught SyntaxError: Identifier 'x' has already been declared<\/code><\/li>\n<\/ul>\n<\/li>\n<li>const\u58f0\u660e\u7684\u53d8\u91cf\uff0c\u58f0\u660e\u65f6\u5fc5\u987b\u521d\u59cb\u5316\uff0c\u65e2\u4e0d\u80fd\u518d\u6b21\u58f0\u660e\uff0c\u4e5f\u4e0d\u53ef\u4ee5\u8fdb\u884c\u66f4\u65b0\uff1b\n<ul>\n<li>\u91cd\u65b0\u58f0\u660e\u4f1a\u62a5\u9519 <code>Uncaught SyntaxError: Identifier 'x' has already been declared<\/code><\/li>\n<li>\u66f4\u65b0\u503c\u4e5f\u4f1a\u62a5\u9519 <code>Uncaught TypeError: Assignment to constant variable.<\/code><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<h3>\u53d8\u91cf\u63d0\u5347\u548cTDZ\uff08Temporal Dead Zone\uff09<\/h3>\n<ul>\n<li>\u4ece\u4f5c\u7528\u57df\u5f00\u59cb\u5230\u53d8\u91cf\u58f0\u660e\u7684\u4f4d\u7f6e\uff0c\u8fd9\u6bb5\u533a\u57df\u5c31\u662f TDZ\u3002<\/li>\n<li>var\u58f0\u660e\u7684\u53d8\u91cf\uff0c\u5b58\u5728\u53d8\u91cf\u63d0\u5347\uff0c\u53d8\u91cf\u5b9a\u4e49\u4e0d\u4f46\u4f1a\u88ab\u63d0\u5347\u5230\u4f5c\u7528\u57df\u7684\u9876\u90e8\uff0c\u800c\u4e14\u8fd8\u4f1a\u521d\u59cb\u5316\u4e3aundefined\uff1b<\/li>\n<li>let\u548cconst\u58f0\u660e\u7684\u53d8\u91cf\uff0c\u4e0d\u5b58\u5728\u53d8\u91cf\u63d0\u5347\uff0c\u5b58\u5728TDZ\u3002\u5982\u679c\u5728\u521d\u59cb\u5316\u4e4b\u524d\u5c31\u4f7f\u7528\uff0c\u4f1a\u62a5\u9519 <code>Uncaught ReferenceError: Cannot access 'x' before initialization<\/code><\/li>\n<\/ul>\n<p>\u6ca1\u9519\uff0c\u90a3\u4e2a\u5c0f\u4f19\u4f34\u5c31\u662f\u6211\u81ea\u5df1\uff1a\uff09<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u4eca\u5929\u53c8\u6709\u5c0f\u4f19\u4f34\u95ee\u6211\u4e00\u4e2a\u8fd9\u6837\u7684\u95ee\u9898\uff0cJavaScript\u4e2d\uff0c\u4e3a\u4ec0\u4e48\u6709\u7684\u53d8\u91cf\u7528var\u5b9a\u4e49\uff0c\u6709\u7684\u7528let\uff0c\u8fd8\u6709\u7684\u7528c<\/p>\n<p><a class=\"moretag\" href=\"https:\/\/www.sunpengcheng.com\/index.php\/2025\/07\/29\/var-let-const\/\">Continue Reading&hellip;<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[65,3],"tags":[],"class_list":["post-574","post","type-post","status-publish","format-standard","hentry","category-dev-skills","category-js"],"_links":{"self":[{"href":"https:\/\/www.sunpengcheng.com\/index.php\/wp-json\/wp\/v2\/posts\/574","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.sunpengcheng.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.sunpengcheng.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.sunpengcheng.com\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.sunpengcheng.com\/index.php\/wp-json\/wp\/v2\/comments?post=574"}],"version-history":[{"count":8,"href":"https:\/\/www.sunpengcheng.com\/index.php\/wp-json\/wp\/v2\/posts\/574\/revisions"}],"predecessor-version":[{"id":582,"href":"https:\/\/www.sunpengcheng.com\/index.php\/wp-json\/wp\/v2\/posts\/574\/revisions\/582"}],"wp:attachment":[{"href":"https:\/\/www.sunpengcheng.com\/index.php\/wp-json\/wp\/v2\/media?parent=574"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.sunpengcheng.com\/index.php\/wp-json\/wp\/v2\/categories?post=574"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.sunpengcheng.com\/index.php\/wp-json\/wp\/v2\/tags?post=574"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}