{"id":124,"date":"2010-09-30T10:56:31","date_gmt":"2010-09-30T10:56:31","guid":{"rendered":"http:\/\/enjoyasp.net\/?p=124"},"modified":"2010-09-30T10:56:31","modified_gmt":"2010-09-30T10:56:31","slug":"js%e6%8b%be%e9%81%972","status":"publish","type":"post","link":"https:\/\/enjoyasp.net\/index.php\/2010\/09\/30\/js%e6%8b%be%e9%81%972\/","title":{"rendered":"JS\u62fe\u90572"},"content":{"rendered":"<p>?\u4e00\u3001\u6570\u636e\u7c7b\u578b<br \/>\n?? \u5728js\u53ea\u6709\u4e94\u79cd\u6570\u636e\u7c7b\u578b\uff0cnull, undefined, String, Number,Object<\/p>\n<p>????? undefined\uff1a\u672a\u5b9a\u4e49\uff0c\u6211\u4eec\u4e5f\u53ef\u79f0\u4e4b\u4e3a\u4e0d\u5b58\u5728\uff0ctypeof(undefined)=undefined.<\/p>\n<p>\u3000\u3000null:\u4e3a\u7a7a\u3002undefined\u662f\u4e0d\u5b58\u5728\uff0c\u800cnull\u662f\u5b58\u5728\uff0c\u4f46\u5374\u65e0\u3002typeof(null)=object,\u4f46null\u53c8\u4e0d\u662fobject\uff0c\u4e14undefined==null<\/p>\n<p>\u3000\u3000boolean:true or false\u3002<\/p>\n<p>\u3000\u3000Number: \u6570\u5b57\u5982\uff1avar s= new Number(20);??? alert(s.toString(2)); \/\/10100? \u63a5\u6536\u65f6\u4e0d\u662f\u7528Number a = new Number(20),\u800c\u662f\u7528var \u8fd9\u6837s\u5c31\u662f\u4e00\u4e2aNumber\u7c7b\u578b\uff0c\u5176\u5c5e\u6027\u6709\uff1aMAX_VALUE \u53ef\u8868\u793a\u7684\u6700\u5927\u7684\u6570\u3002MIN_VALUE \u53ef\u8868\u793a\u7684\u6700\u5c0f\u7684\u6570\u3002 NaN \u975e\u6570\u5b57\u503c\u3002NEGATIVE_INFINITY \u8d1f\u65e0\u7a77\u5927\uff0c\u6ea2\u51fa\u65f6\u8fd4\u56de\u8be5\u503c\u3002POSITIVE_INFINITY \u6b63\u65e0\u7a77\u5927\uff0c\u6ea2\u51fa\u65f6\u8fd4\u56de\u8be5\u503c\u3002 \u65b9\u6cd5\u6709\uff1atoString? \u53ef\u4ee5\u63a5\u53d7\u4e00\u4e2a\u4ece2\u523036\u7684\u6570\u5b57\uff0c\u7136\u540e\u628a\u6211\u4eec\u7684Number\u8f6c\u6362\u4e3a\u76f8\u5e94\u7684\u8fdb\u5236\u6570\u3002<\/p>\n<p>????? \u6ce8\uff1aNaN\u548cInfinity\u662f\u4e24\u4e2a\u7279\u6b8a\u4e4b\u6570\uff0cNaN\u4ee3\u8868\u4e00\u4e2a\u65e0\u6cd5\u7528\u6570\u503c\u6765\u8868\u793a\u7684\u6570\u5b57\uff0c\u800cInfinity\u4ee3\u8868\u4e00\u4e2a\u65e0\u7a77\u5927\u7684\u6570\u5b57\uff0c\u76f8\u5bf9\u7684\uff0c-Infinify\u5219\u4ee3\u8868\u8d1f\u65e0\u7a77\u5927\u3002\u5728\u6b64\u6709\u4e24\u70b9\u7279\u6b8a\u7684\u5730\u65b9\uff1aNaN!=NaN\uff0cInfinity\/Infinity=NaN\u3002<\/p>\n<p>\u3000\u3000String\uff1a\u5b57\u7b26\u4e32\uff0cJavascript\u4e2d\u6ca1\u6709\u5b57\u7b26\u7684\u6982\u5ff5\uff0c\u5b57\u7b26\u4e32\u662f\u8868\u793a\u6587\u672c\u7684\u6700\u5c0f\u5355\u4f4d\u3002\u5728\u5b57\u7b26\u4e32\u4e2d\uff0c\u6709\u8fd9\u6837\u7684\u4e24\u4e2a\u51fd\u6570\uff0c\u5206\u522b\u662fcharAt(index)\u548ccharCodeAt(index)\u5206\u522b\u8fd4\u56de\u5bf9\u5e94\u7d22\u5f15\u7684\u5b57\u7b26\u548c\u5b57\u7b26Unicode\u7f16\u7801\u3002\u5728\u6211\u4eec\u5e73\u65f6\uff0c\u53ef\u80fd\u7ecf\u5e38\u4f1a\u4f7f\u7528\u4e0b\u6807\u7684\u65b9\u5f0f\u8bbf\u95ee\uff0c\u5982s[10]\uff0c\u53ef\u662f\u8fd9\u5e76\u4e0d\u662fECMAScript\u7684\u6807\u51c6\uff0c\u5e94\u8be5\u5c3d\u91cf\u907f\u514d\u3002<\/p>\n<p>\u4e8c\uff0cjs\u5efa\u7acb\u7c7b\u5bf9\u8c61<\/p>\n<p>?1\uff0c\u6210\u5458\u53d8\u91cf\u6743\u9650\u5206\u4e3a\u79c1\u6709\u4e0e\u516c\u6709\u3002\u79c1\u6709\u6307\u7528var\u5efa\u7acb\u7684\u6210\u5458 \uff0c\u516c\u6709\u6307\u7528this\u5efa\u7acb\u7684\u5bf9\u8c61???<\/p>\n<p>var obj = function () {??? var a = 1;??? this.b = 2;??? this.c = 5;??? this.fun = function () {? ?? this.c = a+this.b;??? }};<br \/>\nvar o = new obj(); o.fun();????????? alert(o.b);?? \/\/2 ???????? alert(o.a);? \/\/\u4e0d\u53ef\u8bbf\u95ee\u7ed3\u679c\u4e3aundefined<\/p>\n<p>2,\u4e3a\u7c7b\u52a8\u6001\u589e\u52a0\u53d8\u91cf\uff0c\u51fd\u6570&#8212;prototype<\/p>\n<p>??? var obj = function () {? this.c = 5;};<br \/>\nvar o = new obj(); alert(o.c);? \/\/5<br \/>\n<a href=\"http:\/\/obj.prototype.tt\/\">obj.prototype.tt<\/a> = -3? obj.prototype.setValue = function(){?? this.c = -1; } \/\/\u53ef\u76f4\u63a5\u64cd\u4f5c\u7c7b\u6210\u5458<br \/>\no.setValue(); \/\/\u8bbe\u7f6e\u540e\u76f4\u63a5\u8c03\u7528<\/p>\n<p>alert(o.c);<br \/>\nalert(<a href=\"http:\/\/o.tt\/\">o.tt<\/a>);<\/p>\n<p>\u5229\u7528prototype\u6709\u4e2a\u597d\u5904\uff0c\u5b9a\u4e49\u7684\u4e1c\u897f\u591a\u4e2a\u5b9e\u4f8b\u4e5f\u662f\u5171\u7528\u4e00\u4e2a\u3002\u4e0d\u7136\u76f4\u63a5\u5b9a\u4e49\u65b9\u6cd5\uff0c\u5219\u6bcf\u4e00\u4e2a\u5b9e\u4f8b\u7684\u65b9\u6cd5\u662f\u4e0d\u4e00\u6837\u7684\uff0c\u5b58\u5728\u4e0d\u540c\u7684\u5730\u5740\u4e2d<\/p>\n","protected":false},"excerpt":{"rendered":"<p>?\u4e00\u3001\u6570\u636e\u7c7b\u578b ?? 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