{"id":1460,"date":"2014-03-11T10:49:24","date_gmt":"2014-03-11T02:49:24","guid":{"rendered":"http:\/\/www.gaigaiming.com\/?p=1460"},"modified":"2014-03-11T10:49:24","modified_gmt":"2014-03-11T02:49:24","slug":"js%e5%ad%97%e7%ac%a6%e4%b8%b2%e8%bd%ac%e6%95%b0%e5%ad%97","status":"publish","type":"post","link":"https:\/\/www.gaigaiming.com\/index.php\/2014\/03\/11\/js%e5%ad%97%e7%ac%a6%e4%b8%b2%e8%bd%ac%e6%95%b0%e5%ad%97\/","title":{"rendered":"js\u5b57\u7b26\u4e32\u8f6c\u6570\u5b57"},"content":{"rendered":"

\u65b9\u6cd5\u4e3b\u8981\u6709\u4e09\u79cd
\n\u8f6c\u6362\u51fd\u6570\u3001\u5f3a\u5236\u7c7b\u578b\u8f6c\u6362\u3001\u5229\u7528js\u53d8\u91cf\u5f31\u7c7b\u578b\u8f6c\u6362\u3002<\/p>\n

1. \u8f6c\u6362\u51fd\u6570\uff1a<\/p>\n

js\u63d0\u4f9b\u4e86parseInt()\u548cparseFloat()\u4e24\u4e2a\u8f6c\u6362\u51fd\u6570\u3002\u524d\u8005\u628a\u503c\u8f6c\u6362\u6210\u6574\u6570\uff0c\u540e\u8005\u628a\u503c\u8f6c\u6362\u6210\u6d6e\u70b9\u6570\u3002\u53ea\u6709\u5bf9String\u7c7b\u578b\u8c03\u7528\u8fd9\u4e9b\u65b9\u6cd5\uff0c\u8fd9\u4e24\u4e2a\u51fd\u6570\u624d\u80fd\u6b63\u786e\u8fd0\u884c\uff1b\u5bf9\u5176\u4ed6\u7c7b\u578b\u8fd4\u56de\u7684\u90fd\u662fNaN(Not a Number)\u3002<\/p>\n

\u4e00\u4e9b\u793a\u4f8b\u5982\u4e0b\uff1a<\/p>\n

parseInt(“1234blue”); \/\/returns 1234
\nparseInt(“0xA”); \/\/returns 10
\nparseInt(“22.5”); \/\/returns 22
\nparseInt(“blue”); \/\/returns NaN<\/p>\n

parseInt()\u65b9\u6cd5\u8fd8\u6709\u57fa\u6a21\u5f0f\uff0c\u53ef\u4ee5\u628a\u4e8c\u8fdb\u5236\u3001\u516b\u8fdb\u5236\u3001\u5341\u516d\u8fdb\u5236\u6216\u5176\u4ed6\u4efb\u4f55\u8fdb\u5236\u7684\u5b57\u7b26\u4e32\u8f6c\u6362\u6210\u6574\u6570\u3002\u57fa\u662f\u7531parseInt()\u65b9\u6cd5\u7684\u7b2c\u4e8c\u4e2a\u53c2\u6570\u6307\u5b9a\u7684\uff0c\u793a\u4f8b\u5982\u4e0b\uff1a<\/p>\n

parseInt(“AF”, 16); \/\/returns 175
\nparseInt(“10”, 2); \/\/returns 2
\nparseInt(“10”, 8); \/\/returns 8
\nparseInt(“10”, 10); \/\/returns 10
\n\u5982\u679c\u5341\u8fdb\u5236\u6570\u5305\u542b\u524d\u5bfc0\uff0c\u90a3\u4e48\u6700\u597d\u91c7\u7528\u57fa\u657010\uff0c\u8fd9\u6837\u624d\u4e0d\u4f1a\u610f\u5916\u5730\u5f97\u5230\u516b\u8fdb\u5236\u7684\u503c\u3002\u4f8b\u5982\uff1a
\nparseInt(“010”); \/\/returns 8
\nparseInt(“010”, 8); \/\/returns 8
\nparseInt(“010”, 10); \/\/returns 10<\/p>\n

parseFloat()\u65b9\u6cd5\u4e0eparseInt()\u65b9\u6cd5\u7684\u5904\u7406\u65b9\u5f0f\u76f8\u4f3c\u3002
\n\u4f7f\u7528parseFloat()\u65b9\u6cd5\u7684\u53e6\u4e00\u4e0d\u540c\u4e4b\u5904\u5728\u4e8e\uff0c\u5b57\u7b26\u4e32\u5fc5\u987b\u4ee5\u5341\u8fdb\u5236\u5f62\u5f0f\u8868\u793a\u6d6e\u70b9\u6570\uff0cparseFloat()\u6ca1\u6709\u57fa\u6a21\u5f0f\u3002<\/p>\n

\u4e0b\u9762\u662f\u4f7f\u7528parseFloat()\u65b9\u6cd5\u7684\u793a\u4f8b\uff1a
\nparseFloat(“1234blue”); \/\/returns 1234.0
\nparseFloat(“0xA”); \/\/returns NaN
\nparseFloat(“22.5”); \/\/returns 22.5
\nparseFloat(“22.34.5”); \/\/returns 22.34
\nparseFloat(“0908”); \/\/returns 908
\nparseFloat(“blue”); \/\/returns NaN<\/p>\n

2. \u5f3a\u5236\u7c7b\u578b\u8f6c\u6362<\/p>\n

\u8fd8\u53ef\u4f7f\u7528\u5f3a\u5236\u7c7b\u578b\u8f6c\u6362\uff08type casting\uff09\u5904\u7406\u8f6c\u6362\u503c\u7684\u7c7b\u578b\u3002\u4f7f\u7528\u5f3a\u5236\u7c7b\u578b\u8f6c\u6362\u53ef\u4ee5\u8bbf\u95ee\u7279\u5b9a\u7684\u503c\uff0c\u5373\u4f7f\u5b83\u662f\u53e6\u4e00\u79cd\u7c7b\u578b\u7684\u3002
\nECMAScript\u4e2d\u53ef\u7528\u76843\u79cd\u5f3a\u5236\u7c7b\u578b\u8f6c\u6362\u5982\u4e0b\uff1a
\nBoolean(value)\u2014\u2014\u628a\u7ed9\u5b9a\u7684\u503c\u8f6c\u6362\u6210Boolean\u578b\uff1b
\nNumber(value)\u2014\u2014\u628a\u7ed9\u5b9a\u7684\u503c\u8f6c\u6362\u6210\u6570\u5b57\uff08\u53ef\u4ee5\u662f\u6574\u6570\u6216\u6d6e\u70b9\u6570\uff09\uff1b
\nString(value)\u2014\u2014\u628a\u7ed9\u5b9a\u7684\u503c\u8f6c\u6362\u6210\u5b57\u7b26\u4e32\u3002
\n\u7528\u8fd9\u4e09\u4e2a\u51fd\u6570\u4e4b\u4e00\u8f6c\u6362\u503c\uff0c\u5c06\u521b\u5efa\u4e00\u4e2a\u65b0\u503c\uff0c\u5b58\u653e\u7531\u539f\u59cb\u503c\u76f4\u63a5\u8f6c\u6362\u6210\u7684\u503c\u3002\u8fd9\u4f1a\u9020\u6210\u610f\u60f3\u4e0d\u5230\u7684\u540e\u679c\u3002
\n\u5f53\u8981\u8f6c\u6362\u7684\u503c\u662f\u81f3\u5c11\u6709\u4e00\u4e2a\u5b57\u7b26\u7684\u5b57\u7b26\u4e32\u3001\u975e0\u6570\u5b57\u6216\u5bf9\u8c61\uff08\u4e0b\u4e00\u8282\u5c06\u8ba8\u8bba\u8fd9\u4e00\u70b9\uff09\u65f6\uff0cBoolean()\u51fd\u6570\u5c06\u8fd4\u56detrue\u3002\u5982\u679c\u8be5\u503c\u662f\u7a7a\u5b57\u7b26\u4e32\u3001\u6570\u5b570\u3001undefined\u6216null\uff0c\u5b83\u5c06\u8fd4\u56defalse\u3002<\/p>\n

\u53ef\u4ee5\u7528\u4e0b\u9762\u7684\u4ee3\u7801\u6bb5\u6d4b\u8bd5Boolean\u578b\u7684\u5f3a\u5236\u7c7b\u578b\u8f6c\u6362\u3002<\/p>\n

Boolean(“”); \/\/false \u2013 empty string
\nBoolean(“hi”); \/\/true \u2013 non-empty string
\nBoolean(100); \/\/true \u2013 non-zero number
\nBoolean(null); \/\/false – null
\nBoolean(0); \/\/false – zero
\nBoolean(new Object()); \/\/true \u2013 object<\/p>\n

Number()\u7684\u5f3a\u5236\u7c7b\u578b\u8f6c\u6362\u4e0eparseInt()\u548cparseFloat()\u65b9\u6cd5\u7684\u5904\u7406\u65b9\u5f0f\u76f8\u4f3c\uff0c\u53ea\u662f\u5b83\u8f6c\u6362\u7684\u662f\u6574\u4e2a\u503c\uff0c\u800c\u4e0d\u662f\u90e8\u5206\u503c\u3002\u793a\u4f8b\u5982\u4e0b\uff1a<\/p>\n

\u7528\u3000\u3000\u6cd5 \u7ed3\u3000\u3000\u679c
\nNumber(false) 0
\nNumber(true) 1
\nNumber(undefined) NaN
\nNumber(null) 0
\nNumber( “5.5 “) 5.5
\nNumber( “56 “) 56
\nNumber( “5.6.7 “) NaN
\nNumber(new Object()) NaN
\nNumber(100) 100 <\/p>\n

\u6700\u540e\u4e00\u79cd\u5f3a\u5236\u7c7b\u578b\u8f6c\u6362\u65b9\u6cd5String()\u662f\u6700\u7b80\u5355\u7684\uff0c\u793a\u4f8b\u5982\u4e0b\uff1a<\/p>\n

var s1 = String(null); \/\/”null”
\nvar oNull = null;
\nvar s2 = oNull.toString(); \/\/won\u2019t work, causes an error<\/p>\n

3. \u5229\u7528js\u53d8\u91cf\u5f31\u7c7b\u578b\u8f6c\u6362<\/p>\n

\u4e3e\u4e2a\u5c0f\u4f8b\u5b50\uff0c\u4e00\u770b\uff0c\u5c31\u4f1a\u660e\u767d\u4e86\u3002
\n