{"id":8263,"date":"2023-11-28T20:20:55","date_gmt":"2023-11-28T12:20:55","guid":{"rendered":"https:\/\/wx.kaifamiao.info\/?p=8263"},"modified":"2023-12-04T18:26:19","modified_gmt":"2023-12-04T10:26:19","slug":"vue-zhong-undefinednull-he-undeclared-you-shen-me","status":"publish","type":"post","link":"http:\/\/wx.kaifamiao.info\/index.php\/2023\/11\/28\/vue-zhong-undefinednull-he-undeclared-you-shen-me\/","title":{"rendered":"Vue \u4e2d undefined\uff0cnull \u548c undeclared \u6709\u4ec0\u4e48\u533a\u522b\uff1f"},"content":{"rendered":"<p>\u5728 Vue \u4e2d\uff0c\u4ee5\u53ca JavaScript \u4e2d\uff0c<code>undefined<\/code>\u3001<code>null<\/code> \u548c undeclared\uff08\u672a\u58f0\u660e\uff09\u4ee3\u8868\u7740\u4e0d\u540c\u7684\u6982\u5ff5\u548c\u72b6\u6001\uff1a<\/p>\n<ol>\n<li><strong>undefined\uff1a<\/strong>\n<ul>\n<li>\u8868\u793a\u5df2\u58f0\u660e\u4f46\u672a\u8d4b\u503c\u7684\u53d8\u91cf\uff0c\u9ed8\u8ba4\u7684\u521d\u59cb\u503c\uff0c\u4e5f\u53ef\u4ee5\u901a\u8fc7\u5c06\u53d8\u91cf\u663e\u5f0f\u8d4b\u503c\u4e3a <code>undefined<\/code> \u6765\u8fbe\u5230\u76f8\u540c\u6548\u679c\u3002<\/li>\n<li>\u5728\u4f7f\u7528\u4e2d\uff0c\u901a\u5e38\u8868\u793a\u53d8\u91cf\u5df2\u7ecf\u58f0\u660e\u4f46\u5c1a\u672a\u88ab\u8d4b\u503c\u6216\u8005\u4e0d\u5b58\u5728\u7279\u5b9a\u7684\u5bf9\u8c61\u5c5e\u6027\u3002<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n<pre><code class=\"language-javascript  line-numbers\">let variable; \/\/ declared but not assigned, defaults to undefined\nconsole.log(variable); \/\/ output: undefined\n<\/code><\/pre>\n<ol start=\"2\">\n<li><strong>null\uff1a<\/strong>\n<ul>\n<li>\u8868\u793a\u7a7a\u503c\u6216\u8005\u662f\u88ab\u8d4b\u503c\u4e3a null \u7684\u53d8\u91cf\u3002\u5b83\u662f JavaScript \u4e2d\u7684\u4e00\u4e2a\u7279\u6b8a\u503c\uff0c\u7528\u4e8e\u663e\u793a\u5730\u8868\u793a\u53d8\u91cf\u7684\u7a7a\u503c\u3002<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n<pre><code class=\"language-javascript  line-numbers\">let variable = null; \/\/ assigned as null\nconsole.log(variable); \/\/ output: null\n<\/code><\/pre>\n<ol start=\"3\">\n<li><strong>Undeclared\uff08\u672a\u58f0\u660e\uff09\uff1a<\/strong>\n<ul>\n<li>\u8868\u793a\u5c1a\u672a\u58f0\u660e\u7684\u53d8\u91cf\u6216\u5c1d\u8bd5\u8bbf\u95ee\u4e0d\u5b58\u5728\u7684\u53d8\u91cf\uff0c\u8fd9\u79cd\u60c5\u51b5\u4f1a\u5bfc\u81f4 JavaScript \u629b\u51fa\u9519\u8bef\u3002<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n<pre><code class=\"language-javascript  line-numbers\">\/\/ Attempting to access an undeclared variable will result in a ReferenceError\nconsole.log(nonExistentVariable); \/\/ ReferenceError: nonExistentVariable is not defined\n<\/code><\/pre>\n<p>\u5728 JavaScript \u4e2d\uff0c<code>undefined<\/code> \u548c <code>null<\/code> \u662f\u4e24\u4e2a\u4e0d\u540c\u7684\u503c\uff0c\u5206\u522b\u8868\u793a\u672a\u8d4b\u503c\u548c\u7a7a\u503c\u3002\u800c <code>undeclared<\/code> \u8868\u793a\u5c1a\u672a\u58f0\u660e\u7684\u53d8\u91cf\uff0c\u8bbf\u95ee\u672a\u58f0\u660e\u7684\u53d8\u91cf\u4f1a\u5bfc\u81f4 ReferenceError\u3002\u7406\u89e3\u8fd9\u4e9b\u6982\u5ff5\u6709\u52a9\u4e8e\u5728\u7f16\u5199\u4ee3\u7801\u65f6\u66f4\u597d\u5730\u5904\u7406\u53d8\u91cf\u7684\u72b6\u6001\u548c\u907f\u514d\u6f5c\u5728\u7684\u9519\u8bef\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u5728 Vue \u4e2d\uff0c\u4ee5\u53ca JavaScript \u4e2d\uff0cundefined\u3001null \u548c undeclared\uff08\u672a\u58f0\u660e [&hellip;]<\/p>\n","protected":false},"author":11,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[114],"tags":[],"class_list":["post-8263","post","type-post","status-publish","format-standard","hentry","category-vue"],"_links":{"self":[{"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/posts\/8263","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/users\/11"}],"replies":[{"embeddable":true,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/comments?post=8263"}],"version-history":[{"count":3,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/posts\/8263\/revisions"}],"predecessor-version":[{"id":15359,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/posts\/8263\/revisions\/15359"}],"wp:attachment":[{"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/media?parent=8263"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/categories?post=8263"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/tags?post=8263"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}