Javascript类型检测

1.typeof

typeof 适合基本类型及function检测，遇到null失效。

typeof 100; // "number" typeof true; // "boolean" typeof fun(); // "function" typeof NaN; // "number" typeof undefined; // "undefined" typeof null; // "object" typeof new Object(); // "object" typeof [1,2]; // "object"

2.instanceof

instanceof一般用于对象类型的判断，是基于原型链的判断。

//obj instanceof Object [1,2] instanceof Array === true new Object() instanceof Array === false function Student(){} function Teacher(){} var s = new Student() console.log(s instanceof Student) // true console.log(s instanceof Teacher) // false Student.prototype = new Teacher() var s2 = new Student() console.log(s2 instanceof Student) // true console.log(s2 instanceof Teacher) // true

PS:适合自定义对象，也可以用来检测原生对象。不同window或iframe间的对象类型检测不能用instanceof。

3.Object.prototype.toString.apply()

通过{}.toString拿到，适合内置对象和基本类型，遇到null和undefined失效（IE678返回[object Object]）。

Object.prototype.toString.apply([]) === "[object Array]" Object.prototype.toString.apply(function(){}) === "[object Function]" Object.prototype.toString.apply(null) === "[object Null]" // IE6/7/8返回"[object Object]" Object.prototype.toString.apply(undefined) === "[object Undefined]" Object.prototype.toString.apply(123) === "[object Number]" Object.prototype.toString.apply('123') === "[object String]" Object.prototype.toString.apply(true) === "[object Boolean]" console.log(Object.prototype.toString.apply(new Object())) //[object Object] function Student(){} var s = new Student() console.log(Object.prototype.toString.apply(s)) //[object Object] console.log(Object.prototype.toString.apply(window)) // [object Window] console.log(Object.prototype.toString.apply(new Date())) //[object Date]