{"id":3258,"date":"2014-11-14T14:59:35","date_gmt":"2014-11-14T06:59:35","guid":{"rendered":"https:\/\/sdeno.com\/?p=3258"},"modified":"2014-11-14T14:59:35","modified_gmt":"2014-11-14T06:59:35","slug":"js%e4%b8%adtypeof%e4%b8%8einstanceof%e7%9a%84%e5%8c%ba%e5%88%ab","status":"publish","type":"post","link":"https:\/\/sdeno.com\/?p=3258","title":{"rendered":"JS\u4e2dtypeof\u4e0einstanceof\u7684\u533a\u522b"},"content":{"rendered":"

JavaScript \u4e2d typeof \u548c instanceof \u5e38\u7528\u6765\u5224\u65ad\u4e00\u4e2a\u53d8\u91cf\u662f\u5426\u4e3a\u7a7a\uff0c\u6216\u8005\u662f\u4ec0\u4e48\u7c7b\u578b\u7684\u3002\u4f46\u5b83\u4eec\u4e4b\u95f4\u8fd8\u662f\u6709\u533a\u522b\u7684\uff1a<\/p>\n

typeof<\/strong><\/p>\n

typeof \u662f\u4e00\u4e2a\u4e00\u5143\u8fd0\u7b97\uff0c\u653e\u5728\u4e00\u4e2a\u8fd0\u7b97\u6570\u4e4b\u524d\uff0c\u8fd0\u7b97\u6570\u53ef\u4ee5\u662f\u4efb\u610f\u7c7b\u578b\u3002<\/span><\/p>\n

\u5b83\u8fd4\u56de\u503c\u662f\u4e00\u4e2a\u5b57\u7b26\u4e32\uff0c\u8be5\u5b57\u7b26\u4e32\u8bf4\u660e\u8fd0\u7b97\u6570\u7684\u7c7b\u578b\u3002typeof \u4e00\u822c\u53ea\u80fd\u8fd4\u56de\u5982\u4e0b\u51e0\u4e2a\u7ed3\u679c\uff1a<\/p>\n

number,boolean,string,function,object,undefined<\/span>\u3002\u6211\u4eec\u53ef\u4ee5\u4f7f\u7528 typeof \u6765\u83b7\u53d6\u4e00\u4e2a\u53d8\u91cf\u662f\u5426\u5b58\u5728\uff0c\u5982 if(typeof a!=”undefined”){alert(“ok”)}\uff0c\u800c\u4e0d\u8981\u53bb\u4f7f\u7528 if(a) \u56e0\u4e3a\u5982\u679c a \u4e0d\u5b58\u5728\uff08\u672a\u58f0\u660e\uff09\u5219\u4f1a\u51fa\u9519\uff0c\u5bf9\u4e8e Array,Null \u7b49\u7279\u6b8a\u5bf9\u8c61\u4f7f\u7528 typeof \u4e00\u5f8b\u8fd4\u56de object\uff0c\u8fd9\u6b63\u662f typeof \u7684\u5c40\u9650\u6027\u3002<\/p>\n

<!DOCTYPE html PUBLIC \"-\/\/W3C\/\/DTD XHTML 1.0 Transitional\/\/EN\" \"http:\/\/www.w3.org\/TR\/xhtml1\/DTD\/xhtml1-transitional.dtd\">\r\n<html xmlns=\"http:\/\/www.w3.org\/1999\/xhtml\">\r\n<head>\r\n<meta http-equiv=\"Content-Type\" content=\"text\/html; charset=utf-8\" \/>\r\n<script language=\"javascript\" type=\"text\/javascript\">\r\ndocument.write (\"typeof(1): \"+typeof(1)+\"<br>\");\r\ndocument.write (\"typeof(NaN): \"+typeof(NaN)+\"<br>\");\r\ndocument.write (\"typeof(Number.MIN_VALUE): \"+typeof(Number.MIN_VALUE)+\"<br>\");\r\ndocument.write (\"typeof(Infinity): \"+typeof(Infinity)+\"<br>\");\r\ndocument.write (\"typeof(\\\"123\\\"): \"+typeof(\"123\")+\"<br>\");\r\ndocument.write (\"typeof(true): \"+typeof(true)+\"<br>\");\r\ndocument.write (\"typeof(window): \"+typeof(window)+\"<br>\");\r\ndocument.write (\"typeof(Array()): \"+typeof(new Array())+\"<br>\");\r\ndocument.write (\"typeof(function(){}): \"+typeof(function(){})+\"<br>\");\r\ndocument.write (\"typeof(document): \"+typeof(document)+\"<br>\");\r\ndocument.write (\"typeof(null): \"+typeof(null)+\"<br>\");\r\ndocument.write (\"typeof(eval): \"+typeof(eval)+\"<br>\");\r\ndocument.write (\"typeof(Date): \"+typeof(Date)+\"<br>\");\r\ndocument.write (\"typeof(sss): \"+typeof(sss)+\"<br>\");\r\ndocument.write (\"typeof(undefined): \"+typeof(undefined)+\"<br>\")\r\n<\/script>\r\n<title>javascript\u7c7b\u578b\u6d4b\u8bd5<\/title>\r\n<\/head>\r\n<body>\r\n<\/body>\r\n<\/html><\/pre>\n
instanceof<\/strong><\/p>\n
instance\uff1a\u5b9e\u4f8b,\u4f8b\u5b50<\/p>\n
a instanceof b?alert(“true”):alert(“false”); \/\/a\u662fb\u7684\u5b9e\u4f8b\uff1f\u771f:\u5047<\/p>\n
instanceof \u7528\u4e8e\u5224\u65ad\u4e00\u4e2a\u53d8\u91cf\u662f\u5426\u67d0\u4e2a\u5bf9\u8c61\u7684\u5b9e\u4f8b\uff0c\u5982 var a=new Array();alert(a instanceof Array); \u4f1a\u8fd4\u56de true\uff0c\u540c\u65f6 alert(a instanceof Object) \u4e5f\u4f1a\u8fd4\u56de true;\u8fd9\u662f\u56e0\u4e3a Array \u662f object \u7684\u5b50\u7c7b\u3002\u518d\u5982\uff1afunction test(){};var a=new test();alert(a instanceof test) \u4f1a\u8fd4\u56de<\/p>\n
\u8c08\u5230 instanceof \u6211\u4eec\u8981\u591a\u63d2\u5165\u4e00\u4e2a\u95ee\u9898\uff0c\u5c31\u662f function \u7684 arguments\uff0c\u6211\u4eec\u5927\u5bb6\u4e5f\u8bb8\u90fd\u8ba4\u4e3a arguments \u662f\u4e00\u4e2a Array\uff0c\u4f46\u5982\u679c\u4f7f\u7528 instaceof \u53bb\u6d4b\u8bd5\u4f1a\u53d1\u73b0 arguments \u4e0d\u662f\u4e00\u4e2a Array \u5bf9\u8c61\uff0c\u5c3d\u7ba1\u770b\u8d77\u6765\u5f88\u50cf\u3002<\/p>\n
\u53e6\u5916\uff1a<\/p>\n
\u6d4b\u8bd5 var a=new Array();if (a instanceof Object) alert(‘Y’);else alert(‘N’);<\/p>\n
\u5f97’Y\u2019<\/p>\n
\u4f46 if (window instanceof Object) alert(‘Y’);else alert(‘N’);<\/p>\n
\u5f97’N’<\/p>\n
\u6240\u4ee5\uff0c\u8fd9\u91cc\u7684 instanceof \u6d4b\u8bd5\u7684 object \u662f\u6307 js \u8bed\u6cd5\u4e2d\u7684 object\uff0c\u4e0d\u662f\u6307 dom \u6a21\u578b\u5bf9\u8c61\u3002<\/p>\n
\u4f7f\u7528 typeof \u4f1a\u6709\u4e9b\u533a\u522b<\/p>\n
alert(typeof(window)) \u4f1a\u5f97 object<\/p>\n
http:\/\/blog.sina.com.cn\/s\/blog_532751d90100iv1r.html<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"
JavaScript \u4e2d typeof \u548c instanceof \u5e38\u7528\u6765\u5224\u65ad\u4e00\u4e2a\u53d8\u91cf\u662f\u5426\u4e3a\u7a7a\uff0c\u6216\u8005\u662f\u4ec0\u4e48\u7c7b\u578b\u7684 […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-3258","post","type-post","status-publish","format-standard","hentry","category-wordpress"],"_links":{"self":[{"href":"https:\/\/sdeno.com\/index.php?rest_route=\/wp\/v2\/posts\/3258","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/sdeno.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/sdeno.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/sdeno.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/sdeno.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=3258"}],"version-history":[{"count":0,"href":"https:\/\/sdeno.com\/index.php?rest_route=\/wp\/v2\/posts\/3258\/revisions"}],"wp:attachment":[{"href":"https:\/\/sdeno.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=3258"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/sdeno.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=3258"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/sdeno.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=3258"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}