{"id":685,"date":"2019-12-11T15:30:00","date_gmt":"2019-12-11T07:30:00","guid":{"rendered":"http:\/\/blog.xrhoujie.com\/?p=685"},"modified":"2019-12-11T15:30:00","modified_gmt":"2019-12-11T07:30:00","slug":"js%e4%b8%ad%e5%88%a4%e6%96%adnull%e3%80%81undefined%e4%b8%8enan%e7%9a%84%e6%96%b9%e6%b3%95","status":"publish","type":"post","link":"http:\/\/blog.xrhoujie.com\/?p=685","title":{"rendered":"JS\u4e2d\u5224\u65adnull\u3001undefined\u4e0eNaN\u7684\u65b9\u6cd5"},"content":{"rendered":"<p>\u5728js\u7684\u9ed8\u8ba4\u60c5\u51b5\u4e0b \u6bd4\u5982\u00a0 9\/0\u00a0 \u00a0=&gt; \u7ed3\u679c\u662f\u00a0 Infinity<\/p>\n<p>0\/0 =&gt;NaN<\/p>\n<p>&nbsp;<\/p>\n<p>\u5224\u65adundefined\u7684\u65b9\u6cd5<br \/>\nvar tmp = undefined;<br \/>\nif (typeof(tmp) == &#8220;undefined&#8221;){<br \/>\nalert(&#8220;undefined&#8221;);<br \/>\n}<\/p>\n<p>\u8bf4\u660e\uff1atypeof \u8fd4\u56de\u7684\u662f\u5b57\u7b26\u4e32\uff0c\u6709\u516d\u79cd\u53ef\u80fd\uff1a\u201cnumber\u201d\u3001\u201cstring\u201d\u3001\u201cboolean\u201d\u3001\u201cobject\u201d\u3001\u201cfunction\u201d\u3001\u201cundefined\u201d<\/p>\n<p>\u5224\u65adnull\u7684\u65b9\u6cd5<br \/>\n\u7531\u4e8e\u4ee5\u4e0b\u539f\u56e0\uff1a<\/p>\n<p>console.log(undefined==null) \/\/true<\/p>\n<p>\u6545\u4e0d\u80fd\u4f7f\u7528tmp==null\u7684\u65b9\u6cd5\u5224\u65adnull<\/p>\n<p>\u5224\u65ad\u65b9\u6cd5\u4e3a\u4f7f\u7528\u4e09\u7b49===\uff1a<\/p>\n<p>var tmp = null;<br \/>\nif(tmp===null) alert(&#8216;null&#8217;);<\/p>\n<p>\u5224\u65adNaN\u7684\u65b9\u6cd5<br \/>\nvar tmp = 0\/0;<br \/>\n\/\/NaN\u81ea\u8eab\u4e5f\u4e0d\u7b49\u4e8e\u81ea\u8eab<br \/>\nif(temp!==temp){<br \/>\nalert(&#8220;NaN&#8221;);<br \/>\n}<br \/>\n\u8bf4\u660e\uff1a\u5982\u679c\u628a NaN \u4e0e\u4efb\u4f55\u503c\uff08\u5305\u62ec\u5176\u81ea\u8eab\uff09\u76f8\u6bd4\u5f97\u5230\u7684\u7ed3\u679c\u5747\u662f false\uff0c\u6240\u4ee5\u8981\u5224\u65ad\u67d0\u4e2a\u503c\u662f\u5426\u662f NaN\uff0c\u4e0d\u80fd\u4f7f\u7528 == \u6216 === \u8fd0\u7b97\u7b26\u3002<\/p>\n<p>&nbsp;<\/p>\n<p>if (a_part === Infinity || isNaN(a_part)) {<\/p>\n<p>xxx\u4ee3\u7801\u5185\u5bb9<\/p>\n<p>}<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u5728js\u7684\u9ed8\u8ba4\u60c5\u51b5\u4e0b \u6bd4\u5982\u00a0 9\/0\u00a0 \u00a0=&gt; \u7ed3\u679c\u662f\u00a0 Infinity 0\/0 =&gt;NaN &#038;n [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":180,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[10],"tags":[19],"_links":{"self":[{"href":"http:\/\/blog.xrhoujie.com\/index.php?rest_route=\/wp\/v2\/posts\/685"}],"collection":[{"href":"http:\/\/blog.xrhoujie.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/blog.xrhoujie.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/blog.xrhoujie.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/blog.xrhoujie.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=685"}],"version-history":[{"count":1,"href":"http:\/\/blog.xrhoujie.com\/index.php?rest_route=\/wp\/v2\/posts\/685\/revisions"}],"predecessor-version":[{"id":686,"href":"http:\/\/blog.xrhoujie.com\/index.php?rest_route=\/wp\/v2\/posts\/685\/revisions\/686"}],"wp:featuredmedia":[{"embeddable":true,"href":"http:\/\/blog.xrhoujie.com\/index.php?rest_route=\/wp\/v2\/media\/180"}],"wp:attachment":[{"href":"http:\/\/blog.xrhoujie.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=685"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/blog.xrhoujie.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=685"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/blog.xrhoujie.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=685"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}