{"id":43967,"date":"2023-12-11T15:01:27","date_gmt":"2023-12-11T07:01:27","guid":{"rendered":"https:\/\/wx.kaifamiao.info\/?p=43967"},"modified":"2023-12-11T15:01:27","modified_gmt":"2023-12-11T07:01:27","slug":"js%e7%9a%84%e5%9f%ba%e6%9c%ac%e6%95%b0%e6%8d%ae%e7%b1%bb%e5%9e%8b%e6%9c%89%e5%93%aa%e4%ba%9b%ef%bc%8c%e5%9f%ba%e6%9c%ac%e6%95%b0%e6%8d%ae%e7%b1%bb%e5%9e%8b%e5%92%8c%e5%bc%95%e7%94%a8%e6%95%b0-2","status":"publish","type":"post","link":"http:\/\/wx.kaifamiao.info\/index.php\/2023\/12\/11\/js%e7%9a%84%e5%9f%ba%e6%9c%ac%e6%95%b0%e6%8d%ae%e7%b1%bb%e5%9e%8b%e6%9c%89%e5%93%aa%e4%ba%9b%ef%bc%8c%e5%9f%ba%e6%9c%ac%e6%95%b0%e6%8d%ae%e7%b1%bb%e5%9e%8b%e5%92%8c%e5%bc%95%e7%94%a8%e6%95%b0-2\/","title":{"rendered":"JS\u7684\u57fa\u672c\u6570\u636e\u7c7b\u578b\u6709\u54ea\u4e9b\uff0c\u57fa\u672c\u6570\u636e\u7c7b\u578b\u548c\u5f15\u7528\u6570\u636e\u7c7b\u578b\u7684\u533a\u522b\uff0cNaN\u662f\u4ec0\u4e48\u7684\u7f29\u5199\uff0cJS\u7684\u4f5c\u7528\u57df\u7c7b\u578b\uff0cundefined==null\u8fd4\u56de\u7684\u7ed3\u679c\u662f\u4ec0\u4e48\uff0cundefined\u4e0enull\u7684\u533a\u522b\u5728\u54ea\uff0c\u5199\u4e00\u4e2a\u51fd\u6570\u5224\u65ad\u53d8\u91cf\u7c7b\u578b?"},"content":{"rendered":"

“`” \u53c2\u8003\u56de\u7b54\uff1a<\/p>\n

JS\u7684\u57fa\u672c\u6570\u636e\u7c7b\u578b\u6709\u5b57\u7b26\u4e32\uff0c\u6570\u5b57\uff0c\u5e03\u5c14\uff0c\u6570\u7ec4\uff0c\u5bf9\u8c61\uff0cNull\uff0cUndefined,\u57fa\u672c\u6570\u636e\u7c7b\u578b\u662f\u6309\u503c\u8bbf\u95ee\u7684\uff0c\u4e5f\u5c31\u662f\u8bf4\u6211\u4eec\u53ef\u4ee5\u64cd\u4f5c\u4fdd\u5b58\u5728\u53d8\u91cf\u4e2d\u7684\u5b9e\u9645\u7684\u503c\uff0c<\/p>\n

\u57fa\u672c\u6570\u636e\u7c7b\u578b\u548c\u5f15\u7528\u6570\u636e\u7c7b\u578b\u7684\u533a\u522b\u5982\u4e0b\uff1a<\/p>\n

\u57fa\u672c\u6570\u636e\u7c7b\u578b\u7684\u503c\u662f\u4e0d\u53ef\u53d8\u7684\uff0c\u4efb\u4f55\u65b9\u6cd5\u90fd\u65e0\u6cd5\u6539\u53d8\u4e00\u4e2a\u57fa\u672c\u7c7b\u578b\u7684\u503c\uff0c\u5f53\u8fd9\u4e2a\u53d8\u91cf\u91cd\u65b0\u8d4b\u503c\u540e\u770b\u8d77\u6765\u53d8\u91cf\u7684\u503c\u662f\u6539\u53d8\u4e86\uff0c\u4f46\u662f\u8fd9\u91cc\u53d8\u91cf\u540d\u53ea\u662f\u6307\u5411\u53d8\u91cf\u7684\u4e00\u4e2a\u6307\u9488\uff0c\u6240\u4ee5\u6539\u53d8\u7684\u662f\u6307\u9488\u7684\u6307\u5411\u6539\u53d8\uff0c\u8be5\u53d8\u91cf\u662f\u4e0d\u53d8\u7684\uff0c\u4f46\u662f\u5f15\u7528\u7c7b\u578b\u53ef\u4ee5\u6539\u53d8<\/p>\n

\u57fa\u672c\u6570\u636e\u7c7b\u578b\u4e0d\u53ef\u4ee5\u6dfb\u52a0\u5c5e\u6027\u548c\u65b9\u6cd5\uff0c\u4f46\u662f\u5f15\u7528\u7c7b\u578b\u53ef\u4ee5<\/p>\n

\u57fa\u672c\u6570\u636e\u7c7b\u578b\u7684\u8d4b\u503c\u662f\u7b80\u5355\u8d4b\u503c\uff0c\u5982\u679c\u4ece\u4e00\u4e2a\u53d8\u91cf\u5411\u53e6\u4e00\u4e2a\u53d8\u91cf\u8d4b\u503c\u57fa\u672c\u7c7b\u578b\u7684\u503c\uff0c\u4f1a\u5728\u53d8\u91cf\u5bf9\u8c61\u4e0a\u521b\u5efa\u4e00\u4e2a\u65b0\u503c\uff0c\u7136\u540e\u628a\u8be5\u503c\u590d\u5236\u5230\u4e3a\u65b0\u53d8\u91cf\u5206\u914d\u7684\u4f4d\u7f6e\u4e0a\uff0c\u5f15\u7528\u6570\u636e\u7c7b\u578b\u7684\u8d4b\u503c\u662f\u5bf9\u8c61\u5f15\u7528\uff0c<\/p>\n

\u57fa\u672c\u6570\u636e\u7c7b\u578b\u7684\u6bd4\u8f83\u662f\u503c\u7684\u6bd4\u8f83\uff0c\u5f15\u7528\u7c7b\u578b\u7684\u6bd4\u8f83\u662f\u5f15\u7528\u7684\u6bd4\u8f83\uff0c\u6bd4\u8f83\u5bf9\u8c61\u7684\u5185\u5b58\u5730\u5740\u662f\u5426\u76f8\u540c<\/p>\n

\u57fa\u672c\u6570\u636e\u7c7b\u578b\u662f\u5b58\u653e\u5728\u6808\u533a\u7684\uff0c\u5f15\u7528\u6570\u636e\u7c7b\u578b\u540c\u4e8b\u4fdd\u5b58\u5728\u6808\u533a\u548c\u5806\u533a<\/p>\n

NaN\u662fJS\u4e2d\u7684\u7279\u6b8a\u503c\uff0c\u8868\u793a\u975e\u6570\u5b57\uff0cNaN\u4e0d\u662f\u6570\u5b57\uff0c\u4f46\u662f\u4ed6\u7684\u6570\u636e\u7c7b\u578b\u662f\u6570\u5b57\uff0c\u5b83\u4e0d\u7b49\u4e8e\u4efb\u4f55\u503c\uff0c\u5305\u62ec\u81ea\u8eab\uff0c\u5728\u5e03\u5c14\u8fd0\u7b97\u65f6\u88ab\u5f53\u505afalse\uff0cNaN\u4e0e\u4efb\u4f55\u6570\u8fd0\u7b97\u5f97\u5230\u7684\u7ed3\u679c\u90fd\u662fNaN\uff0c\u515a\u5458\u7b97\u5931\u8d25\u6216\u8005\u8fd0\u7b97\u65e0\u6cd5\u8fd4\u56de\u6b63\u786e\u7684\u6570\u503c\u7684\u5c31\u4f1a\u8fd4\u56deNaN\uff0c\u4e00\u4e9b\u6570\u5b66\u51fd\u6570\u7684\u8fd0\u7b97\u7ed3\u679c\u4e5f\u4f1a\u51fa\u73b0NaN ,<\/p>\n

JS\u7684\u4f5c\u7528\u57df\u7c7b\u578b\uff1a<\/p>\n

\u4e00\u822c\u8ba4\u4e3a\u7684\u4f5c\u7528\u57df\u662f\u8bcd\u6cd5\u4f5c\u7528\u57df\uff0c\u6b64\u5916JS\u8fd8\u63d0\u4f9b\u4e86\u4e00\u4e9b\u52a8\u6001\u6539\u53d8\u4f5c\u7528\u57df\u7684\u65b9\u6cd5\uff0c\u5e38\u89c1\u7684\u4f5c\u7528\u57df\u7c7b\u578b\u6709\uff1a<\/p>\n

\u51fd\u6570\u4f5c\u7528\u57df\uff0c\u5982\u679c\u5728\u51fd\u6570\u5185\u90e8\u6211\u4eec\u7ed9\u672a\u5b9a\u4e49\u7684\u4e00\u4e2a\u53d8\u91cf\u8d4b\u503c\uff0c\u8fd9\u4e2a\u53d8\u91cf\u4f1a\u8f6c\u53d8\u6210\u4e3a\u4e00\u4e2a\u5168\u5c40\u53d8\u91cf\uff0c<\/p>\n

\u5757\u4f5c\u7528\u57df\uff1a\u5757\u4f5c\u7528\u57df\u5427\u6807\u8bc6\u7b26\u9650\u5236\u5728{}\u4e2d\uff0c<\/p>\n

\u6539\u53d8\u51fd\u6570\u4f5c\u7528\u57df\u7684\u65b9\u6cd5\uff1a<\/p>\n

eval\uff08\uff09\uff0c\u8fd9\u4e2a\u65b9\u6cd5\u63a5\u53d7\u4e00\u4e2a\u5b57\u7b26\u4e32\u4f5c\u4e3a\u53c2\u6570\uff0c\u5e76\u5c06\u5176\u4e2d\u7684\u5185\u5bb9\u89c6\u4e3a\u597d\u50cf\u5728\u4e66\u5199\u65f6\u5c31\u5b58\u5728\u4e8e\u7a0b\u5e8f\u4e2d\u8fd9\u4e2a\u4f4d\u7f6e\u7684\u4ee3\u7801\uff0c<\/p>\n

with\u5173\u952e\u5b57\uff1a\u901a\u5e38\u88ab\u5f53\u505a\u91cd\u590d\u5f15\u7528\u540c\u4e00\u4e2a\u5bf9\u8c61\u7684\u591a\u4e2a\u5c5e\u6027\u7684\u5feb\u6377\u65b9\u5f0f<\/p>\n

\u00a0<\/p>\n

undefined\u4e0enull\uff1a\u76ee\u524dnull\u548cundefined\u57fa\u672c\u662f\u540c\u4e49\u7684\uff0c\u53ea\u6709\u4e00\u4e9b\u7ec6\u5fae\u7684\u5dee\u522b\uff0cnull\u8868\u793a\u6ca1\u6709\u5bf9\u8c61\uff0cundefined\u8868\u793a\u7f3a\u5c11\u503c\uff0c\u5c31\u662f\u6b64\u5904\u5e94\u8be5\u6709\u4e00\u4e2a\u503c\u4f46\u662f\u8fd8\u6ca1\u6709\u5b9a\u4e49\uff0c\u56e0\u6b64undefined==null\u8fd4\u56defalse<\/p>\n

\u6b64\u5916\u4e86\u89e3== \u548c===\u7684\u533a\u522b\uff1a<\/p>\n

\u5728\u505a==\u6bd4\u8f83\u65f6\u3002\u4e0d\u540c\u7c7b\u578b\u7684\u6570\u636e\u4f1a\u5148\u8f6c\u6362\u6210\u4e00\u81f4\u540e\u5728\u505a\u6bd4\u8f83\uff0c===\u4e2d\u5982\u679c\u7c7b\u578b\u4e0d\u4e00\u81f4\u5c31\u76f4\u63a5\u8fd4\u56defalse\uff0c\u4e00\u81f4\u7684\u624d\u4f1a\u6bd4\u8f83<\/p>\n

\u7c7b\u578b\u5224\u65ad\u51fd\u6570\uff0c\u4f7f\u7528typeof\u5373\u53ef\uff0c\u9996\u5148\u5224\u65ad\u662f\u5426\u4e3anull\uff0c\u4e4b\u540e\u7528typeof\u54e6\u6309\u6bb5\uff0c\u5982\u679c\u662fobject\u7684\u8bdd\uff0c\u518d\u7528array.isarray\u5224\u65ad\u662f\u5426\u4e3a\u6570\u7ec4\uff0c\u5982\u679c\u662f\u6570\u5b57\u7684\u8bdd\u7528isNaN\u5224\u65ad\u662f\u5426\u662fNaN\u5373\u53ef
\n\u6269\u5c55\u5b66\u4e60\uff1a<\/p>\n

JS\u91c7\u7528\u7684\u662f\u8bcd\u6cd5\u4f5c\u7528\u57df\uff0c\u4e5f\u5c31\u662f\u9759\u6001\u4f5c\u7528\u57df\uff0c\u6240\u4ee5\u51fd\u6570\u7684\u4f5c\u7528\u57df\u5728\u51fd\u6570\u5b9a\u4e49\u7684\u65f6\u5019\u5c31\u51b3\u5b9a\u4e86\uff0c<\/p>\n

\u770b\u5982\u4e0b\u4f8b\u5b50\uff1a<\/p>\n

<pre><code>var value = 1;
\nfunction foo() {
\nconsole.log(value);
\n}
\nfunction bar() {
\nvar value = 2;
\nfoo();
\n}
\nbar();
\n<\/code><\/pre><\/p>\n

\u5047\u8bbeJavaScript\u91c7\u7528\u9759\u6001\u4f5c\u7528\u57df\uff0c\u8ba9\u6211\u4eec\u5206\u6790\u4e0b\u6267\u884c\u8fc7\u7a0b\uff1a<\/p>\n

\u6267\u884cfoo \u51fd\u6570\uff0c\u5148\u4ece foo \u51fd\u6570\u5185\u90e8\u67e5\u627e\u662f\u5426\u6709\u5c40\u90e8\u53d8\u91cf value\uff0c\u5982\u679c\u6ca1\u6709\uff0c\u5c31\u6839\u636e\u4e66\u5199\u7684\u4f4d\u7f6e\uff0c\u67e5\u627e\u4e0a\u9762\u4e00\u5c42\u7684\u4ee3\u7801\uff0c\u4e5f\u5c31\u662f value \u7b49\u4e8e 1\uff0c\u6240\u4ee5\u7ed3\u679c\u4f1a\u6253\u5370 1\u3002<\/p>\n

\u5047\u8bbeJavaScript\u91c7\u7528\u52a8\u6001\u4f5c\u7528\u57df\uff0c\u8ba9\u6211\u4eec\u5206\u6790\u4e0b\u6267\u884c\u8fc7\u7a0b\uff1a<\/p>\n

\u6267\u884cfoo \u51fd\u6570\uff0c\u4f9d\u7136\u662f\u4ece foo \u51fd\u6570\u5185\u90e8\u67e5\u627e\u662f\u5426\u6709\u5c40\u90e8\u53d8\u91cf value\u3002\u5982\u679c\u6ca1\u6709\uff0c\u5c31\u4ece\u8c03\u7528\u51fd\u6570\u7684\u4f5c\u7528\u57df\uff0c\u4e5f\u5c31\u662f bar \u51fd\u6570\u5185\u90e8\u67e5\u627e value \u53d8\u91cf\uff0c\u6240\u4ee5\u7ed3\u679c\u4f1a\u6253\u5370 2\u3002<\/p>\n

\u524d\u9762\u6211\u4eec\u5df2\u7ecf\u8bf4\u4e86\uff0cJavaScript\u91c7\u7528\u7684\u662f\u9759\u6001\u4f5c\u7528\u57df\uff0c\u6240\u4ee5\u8fd9\u4e2a\u4f8b\u5b50\u7684\u7ed3\u679c\u662f 1\u3002<\/p>\n

<pre><code> "“`
\n<\/code><\/pre>\n","protected":false},"excerpt":{"rendered":"

“`” \u53c2\u8003\u56de\u7b54\uff1a JS\u7684\u57fa\u672c\u6570\u636e\u7c7b\u578b\u6709\u5b57\u7b26\u4e32\uff0c\u6570\u5b57\uff0c\u5e03\u5c14\uff0c\u6570\u7ec4\uff0c\u5bf9\u8c61\uff0cNull\uff0cUn […]<\/p>\n","protected":false},"author":7,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[101],"tags":[],"class_list":["post-43967","post","type-post","status-publish","format-standard","hentry","category-c"],"_links":{"self":[{"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/posts\/43967","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\/7"}],"replies":[{"embeddable":true,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/comments?post=43967"}],"version-history":[{"count":1,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/posts\/43967\/revisions"}],"predecessor-version":[{"id":43968,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/posts\/43967\/revisions\/43968"}],"wp:attachment":[{"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/media?parent=43967"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/categories?post=43967"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/tags?post=43967"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}