typeof function

typeof(para)  會回傳 para 的型別

可能的回傳值有 "number"、"string"、"boolean"、"object"、"function" 和 "undefined"

以下是例子

document.writeln(typeof(1)); // number
document.writeln(typeof("str")); // string
document.writeln(typeof(true)); // boolean
document.writeln(typeof({})); // object
document.writeln(typeof([])); // object
document.writeln(typeof(function(){})); // function


document.writeln(typeof(new Number(1))); // object
document.writeln(typeof(new String("str"))); // object
document.writeln(typeof(new Boolean(true))); // object
document.writeln(typeof(new Object())); // object
document.writeln(typeof(new Array())); // object
document.writeln(typeof(new Function())); // function


document.writeln(1 == new Number(1)); // true
document.writeln("str" == new String("str")); // true
document.writeln(true == new Boolean(true)); // true


document.writeln(typeof(new Number(1) + 0)); // number
document.writeln(typeof(new Number(1).valueOf())); // number
document.writeln(typeof(new String("str").valueOf())); // string
document.writeln(typeof(new Boolean(true).valueOf())); // boolean


Reference:

  http://www.jb51.net/article/16342_2.htm

  http://ticore.blogspot.tw/2008/05/javascript-typeof-oddity.html