{"id":11843,"date":"2023-11-28T22:35:30","date_gmt":"2023-11-28T14:35:30","guid":{"rendered":"https:\/\/wx.kaifamiao.info\/?p=11843"},"modified":"2023-11-30T18:30:20","modified_gmt":"2023-11-30T10:30:20","slug":"javascript-zhong-undefined-he-null-you-shen-me-qu","status":"publish","type":"post","link":"http:\/\/wx.kaifamiao.info\/index.php\/2023\/11\/28\/javascript-zhong-undefined-he-null-you-shen-me-qu\/","title":{"rendered":"JavaScript \u4e2d undefined \u548c null \u6709\u4ec0\u4e48\u533a\u522b\uff1f"},"content":{"rendered":"<p>\u5728 JavaScript \u4e2d\uff0c<code>undefined<\/code> \u548c <code>null<\/code> \u90fd\u662f\u8868\u793a\u65e0\u503c\u7684\u7279\u6b8a\u503c\uff0c\u4f46\u5b83\u4eec\u6709\u4e00\u4e9b\u533a\u522b\uff1a<\/p>\n<ol>\n<li>\n<p><strong><code>undefined<\/code>\uff1a<\/strong><\/p>\n<ul>\n<li>\u8868\u793a\u672a\u5b9a\u4e49\u6216\u672a\u8d4b\u503c\u7684\u53d8\u91cf\uff0c\u8868\u793a\u53d8\u91cf\u58f0\u660e\u4f46\u672a\u521d\u59cb\u5316\u65f6\u7684\u9ed8\u8ba4\u503c\u3002<\/li>\n<li>\u5982\u679c\u53d8\u91cf\u58f0\u660e\u4f46\u672a\u8d4b\u503c\uff0c\u6216\u8005\u8bbf\u95ee\u5bf9\u8c61\u4e0d\u5b58\u5728\u7684\u5c5e\u6027\uff0c\u8fd4\u56de\u7684\u503c\u4e3a <code>undefined<\/code>\u3002<\/li>\n<li>\u4f8b\u5982\uff1a\n<pre><code class=\"language-javascript\">let x;\nconsole.log(x); \/\/ \u8f93\u51fa undefined\n\nlet obj = {};\nconsole.log(obj.nonExistentProperty); \/\/ \u8f93\u51fa undefined\n<\/code><\/pre>\n<\/li>\n<\/ul>\n<\/li>\n<li>\n<p><strong><code>null<\/code>\uff1a<\/strong><\/p>\n<ul>\n<li>\u8868\u793a\u7a7a\u503c\u6216\u8005\u8bf4\u8868\u793a\u53d8\u91cf\u88ab\u8d4b\u503c\u4e3a\u4e00\u4e2a\u7a7a\u5bf9\u8c61\u5f15\u7528\u3002<\/li>\n<li>\u901a\u5e38\u7528\u4e8e\u624b\u52a8\u5c06\u53d8\u91cf\u8bbe\u7f6e\u4e3a\u7a7a\u503c\uff0c\u8868\u793a\u53d8\u91cf\u7684\u503c\u4e3a\u201c\u65e0\u201d\u6216\u201c\u7a7a\u201d\u3002<\/li>\n<li>\u4f8b\u5982\uff1a\n<pre><code class=\"language-javascript\">let y = null;\nconsole.log(y); \/\/ \u8f93\u51fa null\n<\/code><\/pre>\n<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n<h3><a id=\"%E4%B8%BB%E8%A6%81%E5%8C%BA%E5%88%AB%EF%BC%9A\" class=\"anchor\" aria-hidden=\"true\"><span class=\"octicon octicon-link\"><\/span><\/a>\u4e3b\u8981\u533a\u522b\uff1a<\/h3>\n<ul>\n<li><code>undefined<\/code> \u662f\u8868\u793a\u53d8\u91cf\u672a\u521d\u59cb\u5316\u6216\u8005\u4e0d\u5b58\u5728\u7684\u9ed8\u8ba4\u503c\uff0c\u800c <code>null<\/code> \u5219\u662f\u8868\u793a\u53d8\u91cf\u5df2\u7ecf\u88ab\u8d4b\u503c\u4e3a\u7a7a\u503c\u7684\u7279\u6b8a\u503c\u3002<\/li>\n<li><code>undefined<\/code> \u901a\u5e38\u662f\u7531 JavaScript \u5f15\u64ce\u81ea\u52a8\u751f\u6210\u7684\uff0c\u800c <code>null<\/code> \u901a\u5e38\u662f\u5728\u4ee3\u7801\u4e2d\u663e\u5f0f\u8d4b\u503c\u7684\u3002<\/li>\n<\/ul>\n<p>\u5728\u903b\u8f91\u4e0a\uff0c<code>undefined<\/code> \u8868\u793a\u201c\u6ca1\u6709\u503c\u201d\uff0c\u800c <code>null<\/code> \u8868\u793a\u201c\u7a7a\u503c\u201d\u6216\u201c\u503c\u4e3a null\u201d\u3002\u5728\u5927\u591a\u6570\u60c5\u51b5\u4e0b\uff0c<code>undefined<\/code> \u548c <code>null<\/code> \u53ef\u4ee5\u4e92\u6362\u4f7f\u7528\uff0c\u4f46\u5728\u67d0\u4e9b\u60c5\u51b5\u4e0b\uff0c\u9700\u8981\u6839\u636e\u8bed\u4e49\u7684\u9700\u8981\u9009\u62e9\u4f7f\u7528\u5408\u9002\u7684\u503c\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u5728 JavaScript \u4e2d\uff0cundefined \u548c null \u90fd\u662f\u8868\u793a\u65e0\u503c\u7684\u7279\u6b8a\u503c\uff0c\u4f46\u5b83\u4eec\u6709\u4e00\u4e9b\u533a\u522b\uff1a un [&hellip;]<\/p>\n","protected":false},"author":11,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[115],"tags":[],"class_list":["post-11843","post","type-post","status-publish","format-standard","hentry","category-javascript"],"_links":{"self":[{"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/posts\/11843","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=11843"}],"version-history":[{"count":2,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/posts\/11843\/revisions"}],"predecessor-version":[{"id":13634,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/posts\/11843\/revisions\/13634"}],"wp:attachment":[{"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/media?parent=11843"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/categories?post=11843"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/tags?post=11843"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}