{"id":4045,"date":"2024-11-10T10:26:19","date_gmt":"2024-11-10T02:26:19","guid":{"rendered":"https:\/\/fwq.ai\/blog\/4045\/"},"modified":"2024-11-10T10:26:19","modified_gmt":"2024-11-10T02:26:19","slug":"javascript-%e4%b8%ad-var-%e5%92%8c-let-%e6%9c%89%e4%bb%80%e4%b9%88%e5%8c%ba%e5%88%ab%ef%bc%9f","status":"publish","type":"post","link":"https:\/\/fwq.ai\/blog\/4045\/","title":{"rendered":"JavaScript \u4e2d var \u548c let \u6709\u4ec0\u4e48\u533a\u522b\uff1f"},"content":{"rendered":"<p><img decoding=\"async\" src=\"https:\/\/img.php.cn\/upload\/article\/001\/246\/273\/173121624457150.jpg\" class=\"aligncenter\" title=\"JavaScript \u4e2d var \u548c let \u6709\u4ec0\u4e48\u533a\u522b\uff1f\u63d2\u56fe\" alt=\"JavaScript \u4e2d var \u548c let \u6709\u4ec0\u4e48\u533a\u522b\uff1f\u63d2\u56fe\" \/><\/p>\n<p><strong>javascript \u4e2d var \u548c let \u7684<\/strong><\/p>\n<p>\u5728 javascript \u4e2d\uff0c\u4f7f\u7528 var \u548c let \u5173\u952e\u5b57\u53ef\u4ee5\u58f0\u660e\u548c\u5b9a\u4e49\u53d8\u91cf\u3002\u7136\u800c\uff0c\u8fd9\u4e24\u4e2a\u5173\u952e\u5b57\u4e4b\u95f4\u5b58\u5728\u7740\u4e00\u4e9b\u5173\u952e\u7684\u533a\u522b\uff1a<\/p>\n<p><strong><\/strong><\/p>\n<ul>\n<li> <strong>var\uff1a<\/strong>\u58f0\u660e\u7684\u53d8\u91cf\u5177\u6709\u5168\u5c40\u4f5c\u7528\u57df\uff0c\u8fd9\u610f\u5473\u7740\u53ef\u4ee5\u5728\u4ee3\u7801\u7684\u4efb\u4f55\u4f4d\u7f6e\u8bbf\u95ee\u8fd9\u4e9b\u53d8\u91cf\u3002<\/li>\n<li> <strong>let\uff1a<\/strong>\u58f0\u660e\u7684\u53d8\u91cf\u5177\u6709\u5c40\u90e8\u4f5c\u7528\u57df\uff0c\u8fd9\u610f\u5473\u7740\u53ea\u80fd\u5728\u5b9a\u4e49\u5b83\u4eec\u7684\u5757\u5185\u8bbf\u95ee\u8fd9\u4e9b\u53d8\u91cf\u3002<\/li>\n<\/ul>\n<p><strong>\u91cd\u65b0\u58f0\u660e<\/strong><\/p>\n<p><span>\u7acb\u5373\u5b66\u4e60<\/span>\u201c\u201d\uff1b<\/p>\n<ul>\n<li> <strong>var\uff1a<\/strong>\u53ef\u4ee5\u591a\u6b21\u91cd\u65b0\u58f0\u660e\uff08\u4f46\u5728\u540c\u4e00\u4f5c\u7528\u57df\u5185\uff09\u5177\u6709\u76f8\u540c\u540d\u79f0\u7684\u53d8\u91cf\u3002<\/li>\n<li> <strong>let\uff1a<\/strong>\u5728\u540c\u4e00\u4f5c\u7528\u57df\u5185\u91cd\u590d\u58f0\u660e\u5177\u6709\u76f8\u540c\u540d\u79f0\u7684\u53d8\u91cf\u4f1a\u62a5\u9519\u3002<\/li>\n<\/ul>\n<p><strong>\u91cd\u65b0\u8d4b\u503c<\/strong><\/p>\n<ul>\n<li> <strong>var\uff1a<\/strong>\u58f0\u660e\u7684\u53d8\u91cf\u53ef\u4ee5\u88ab\u91cd\u65b0\u8d4b\u503c\u3002<\/li>\n<li> <strong>let\uff1a<\/strong>\u58f0\u660e\u7684\u53d8\u91cf\u4e5f\u53ef\u4ee5\u88ab\u91cd\u65b0\u8d4b\u503c\u3002<\/li>\n<\/ul>\n<p><strong>\u5e38\u91cf<\/strong><\/p>\n<p>javascript \u8fd8\u63d0\u4f9b\u4e86\u4e00\u4e2a const \u5173\u952e\u5b57\uff0c\u7528\u4e8e\u58f0\u660e\u5e38\u91cf\u53d8\u91cf\u3002\u5e38\u91cf\u53d8\u91cf\u4e0d\u80fd\u88ab\u91cd\u65b0\u8d4b\u503c\uff0c\u5e76\u4e14\u5177\u6709\u4e0e let \u76f8\u540c\u7684\u4f5c\u7528\u57df\uff08\u5373\u5c40\u90e8\uff09\u3002<\/p>\n<p>\u4ee5\u4e0b\u662f\u4e00\u4e2a\u7b80\u5355\u7684\u793a\u4f8b\uff0c\u6765\u8bf4\u660e var \u548c let \u4e4b\u95f4\u7684\u533a\u522b\uff1a<\/p>\n<pre>\/\/ \u4f7f\u7528 var \u58f0\u660e\u5168\u5c40\u53d8\u91cf\nvar x = 10;\n\n\/\/ \u5728\u51fd\u6570\u5185\u4f7f\u7528 var \u58f0\u660e\u5c40\u90e8\u53d8\u91cf\nfunction test() {\n  var y = 20;\n  console.log(x); \/\/ 10\uff08\u8bbf\u95ee\u5168\u5c40\u53d8\u91cf\uff09\n  console.log(y); \/\/ 20\uff08\u8bbf\u95ee\u5c40\u90e8\u53d8\u91cf\uff09\n}\n\ntest();\n\n\/\/ \u5728\u51fd\u6570\u5916\u8bbf\u95ee\u5c40\u90e8\u53d8\u91cf\u5c06\u5bfc\u81f4\u9519\u8bef\nconsole.log(y); \/\/ referenceerror: y is not defined<\/pre>\n<p> \u767b\u5f55\u540e\u590d\u5236 <\/p>\n<p>\u800c\u5728\u4ee5\u4e0b\u793a\u4f8b\u4e2d\uff0c\u4f7f\u7528 let \u58f0\u660e\u5c40\u90e8\u53d8\u91cf\uff1a<\/p>\n<pre>\/\/ \u4f7f\u7528 let \u58f0\u660e\u5c40\u90e8\u53d8\u91cf\nfunction test() {\n  let x = 10; \/\/ \u5c40\u90e8\u53d8\u91cf x\n  console.log(x); \/\/ 10\n}\n\ntest();\n\n\/\/ \u5728\u51fd\u6570\u5916\u8bbf\u95ee\u5c40\u90e8\u53d8\u91cf\u5c06\u5bfc\u81f4\u9519\u8bef\nconsole.log(x); \/\/ ReferenceError: x is not defined<\/pre>\n<p> \u767b\u5f55\u540e\u590d\u5236 <\/p>\n<p>\u5728\u8fd9\u4e2a\u793a\u4f8b\u4e2d\uff0c\u51fd\u6570 test() \u5185\u58f0\u660e\u7684\u53d8\u91cf x \u4ec5\u5728\u8be5\u51fd\u6570\u5185\u53ef\u7528\uff0c\u800c\u5728\u51fd\u6570\u5916\u90e8\u8bbf\u95ee\u8be5\u53d8\u91cf\u4f1a\u5f15\u53d1\u9519\u8bef\u3002<\/p>\n<p>\u4ee5\u4e0a\u5c31\u662fJavaScript \u4e2d var \u548c let \u6709\u4ec0\u4e48\uff1f\u7684\u8be6\u7ec6\u5185\u5bb9\uff0c\u66f4\u591a\u8bf7\u5173\u6ce8\u7c73\u4e91\u5176\u5b83\u76f8\u5173\u6587\u7ae0\uff01<\/p>\n","protected":false},"excerpt":{"rendered":"<p>javascript \u4e2d var \u548c let \u7684 \u5728 javascript \u4e2d\uff0c\u4f7f\u7528 var \u548c let \u5173\u952e\u5b57\u53ef\u4ee5\u58f0\u660e\u548c\u5b9a\u4e49\u53d8\u91cf\u3002\u7136\u800c\uff0c\u8fd9\u4e24\u4e2a\u5173\u952e\u5b57\u4e4b\u95f4\u5b58\u5728\u7740\u4e00\u4e9b\u5173\u952e\u7684\u533a\u522b\uff1a var\uff1a\u58f0\u660e\u7684\u53d8\u91cf\u5177\u6709\u5168\u5c40\u4f5c\u7528\u57df\uff0c\u8fd9\u610f\u5473\u7740\u53ef\u4ee5\u5728\u4ee3\u7801\u7684\u4efb\u4f55\u4f4d\u7f6e\u8bbf\u95ee\u8fd9\u4e9b\u53d8\u91cf\u3002 let\uff1a\u58f0\u660e\u7684\u53d8\u91cf\u5177\u6709\u5c40\u90e8\u4f5c\u7528\u57df\uff0c\u8fd9\u610f\u5473\u7740\u53ea\u80fd\u5728\u5b9a\u4e49\u5b83\u4eec\u7684\u5757\u5185\u8bbf\u95ee\u8fd9\u4e9b\u53d8\u91cf\u3002 \u91cd\u65b0\u58f0\u660e \u7acb\u5373\u5b66\u4e60\u201c\u201d\uff1b var\uff1a\u53ef\u4ee5\u591a\u6b21\u91cd\u65b0\u58f0\u660e\uff08\u4f46\u5728\u540c\u4e00\u4f5c\u7528\u57df\u5185\uff09\u5177\u6709\u76f8\u540c\u540d\u79f0\u7684\u53d8\u91cf\u3002 let\uff1a\u5728\u540c\u4e00\u4f5c\u7528\u57df\u5185\u91cd\u590d\u58f0\u660e\u5177\u6709\u76f8\u540c\u540d\u79f0\u7684\u53d8\u91cf\u4f1a\u62a5\u9519\u3002 \u91cd\u65b0\u8d4b\u503c var\uff1a\u58f0\u660e\u7684\u53d8\u91cf\u53ef\u4ee5\u88ab\u91cd\u65b0\u8d4b\u503c\u3002 let\uff1a\u58f0\u660e\u7684\u53d8\u91cf\u4e5f\u53ef\u4ee5\u88ab\u91cd\u65b0\u8d4b\u503c\u3002 \u5e38\u91cf javascript \u8fd8\u63d0\u4f9b\u4e86\u4e00\u4e2a const \u5173\u952e\u5b57\uff0c\u7528\u4e8e\u58f0\u660e\u5e38\u91cf\u53d8\u91cf\u3002\u5e38\u91cf\u53d8\u91cf\u4e0d\u80fd\u88ab\u91cd\u65b0\u8d4b\u503c\uff0c\u5e76\u4e14\u5177\u6709\u4e0e let \u76f8\u540c\u7684\u4f5c\u7528\u57df\uff08\u5373\u5c40\u90e8\uff09\u3002 \u4ee5\u4e0b\u662f\u4e00\u4e2a\u7b80\u5355\u7684\u793a\u4f8b\uff0c\u6765\u8bf4\u660e var \u548c let \u4e4b\u95f4\u7684\u533a\u522b\uff1a \/\/ \u4f7f\u7528 var \u58f0\u660e\u5168\u5c40\u53d8\u91cf var x = 10; \/\/ \u5728\u51fd\u6570\u5185\u4f7f\u7528 var \u58f0\u660e\u5c40\u90e8\u53d8\u91cf function test() { var y = 20; console.log(x); \/\/ [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[16],"tags":[],"class_list":["post-4045","post","type-post","status-publish","format-standard","hentry","category-16"],"_links":{"self":[{"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/posts\/4045","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/comments?post=4045"}],"version-history":[{"count":0,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/posts\/4045\/revisions"}],"wp:attachment":[{"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/media?parent=4045"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/categories?post=4045"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/tags?post=4045"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}