\u5728\u7406\u89e3undefined\u548cnull\u7684\u5dee\u5f02\u4e4b\u524d\uff0c\u6211\u4eec\u5148\u6765\u770b\u770b\u5b83\u4eec\u7684\u76f8\u4f3c\u70b9\u3002
\n\u5b83\u4eec\u90fd\u5c5e\u4e8eJavaScript\u76847\u79cd\u57fa\u672c\u7c7b\u578b\u3002
\nlet primitiveTypes = [‘string’number’,’null’undefined’,’boolean’symbol’, ‘bigint’];
\n\u5b83\u4eec\u662f\u5c5e\u4e8efalsy\u503c\u7c7b\u578b\uff0c\u53ef\u4ee5\u4f7f\u7528Boolean (value)\u6216\uff01\uff01 value\u5c06\u5176\u8f6c\u6362\u4e3a\u5e03\u5c14\u503c\u65f6\uff0c\u503c \u4e3a false
\nconsole. log(!!null)\uff1b \/\/ false
\nconsole. log(!!undefined)\uff1b \/\/ false
\nconsole. log(Boolean(null))\uff1b \/\/ false
\nconsole. log(Boolean(undefined))\uff1b \/\/ false
\n\u63a5\u7740\u6765\u770b\u770b\u5b83\u4eec\u7684\u533a\u522b\u3002
\nundefined\u662f\u672a\u6307\u5b9a\u7279\u5b9a\u503c\u7684\u53d8\u91cf\u7684\u9ed8\u8ba4\u503c\uff0c\u6216\u8005\u6ca1\u6709\u663e\u5f0f\u8fd4\u56de\u503c\u7684\u51fd\u6570\uff0c\u5982:console. log(l), \u8fd8\u5305\u62ec\u5bf9\u8c61\u4e2d\u4e0d\u5b58\u5728\u7684\u5c5e\u6027\uff0c\u8fd9\u4e9bJS\u5f15\u64ce\u90fd\u4f1a\u4e3a\u5176\u5206\u914dundefined\u503c\u3002
\nlet _thisIsUndefined\uff1b
\nconst doNothing = () => {}\uff1b
\nconst someObj = {<\/p>\n
a : ay ,
\nb : "bee",
\nc : "si"
\n};
\nconsole. log(_thisIsUndefined) \uff1b \/\/ undefined
\nconsole. log(doNothing())\uff1b \/\/ undefined
\nconsole. log(someObj["d"])\uff1b \/\/ undefined
\nnull\u662f\u300e\u4e0d\u4ee3\u8868\u4efb\u4f55\u503c\u7684\u503c\u300f\u3002null\u662f\u5df2\u660e\u786e\u5b9a\u4e49\u7ed9\u53d8\u91cf\u7684\u503c\u3002\u5728\u6b64\u793a\u4f8b\u4e2d\uff0c\u5f53
\n\u65b9\u6cd5\u672a\u5f15\u53d1\u9519\u8bef\u65f6\uff0c\u6211\u4eec\u5c06\u83b7\u5f97null\u503c\u3002
\nfs. readFile(‘path\/to\/file’\uff0c(e,data) => {
\nconsole. log(e) \uff1b \/\/\u5f53\u6ca1\u6709\u9519\u8bef\u53d1\u751f\u65f6\uff0c\u6253\u5370null
\nif(e) {
\nconsole. log(e)\uff1b
\n}
\nconsole. log(data);
\n});
\n\u5728\u6bd4\u8f83null\u548cundefined\u65f6\uff0c\u6211\u4eec\u4f7f\u7528==\u65f6\u5f97\u5230true,\u4f7f\u7528===\u65f6\u5f97\u5230false\uff1a
\nconsole. log(null = undefined)\uff1b \/\/ true
\nconsole. log (null == undefined) \uff1b \/\/ false<\/p>\n","protected":false},"excerpt":{"rendered":"
\u5728\u7406\u89e3undefined\u548cnull\u7684\u5dee\u5f02\u4e4b\u524d\uff0c\u6211\u4eec\u5148\u6765\u770b\u770b\u5b83\u4eec\u7684\u76f8\u4f3c\u70b9\u3002 \u5b83\u4eec\u90fd\u5c5e\u4e8eJavaScript\u76847\u79cd […]<\/p>\n","protected":false},"author":8,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[103],"tags":[],"class_list":["post-11653","post","type-post","status-publish","format-standard","hentry","category-qianduan"],"_links":{"self":[{"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/posts\/11653","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\/8"}],"replies":[{"embeddable":true,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/comments?post=11653"}],"version-history":[{"count":1,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/posts\/11653\/revisions"}],"predecessor-version":[{"id":11654,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/posts\/11653\/revisions\/11654"}],"wp:attachment":[{"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/media?parent=11653"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/categories?post=11653"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/tags?post=11653"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}