关于javascript 里面类型的判断

javacript至今共有7中类型

Six data types that are primitives:

1. Boolean
2. Null
3. Undefined
4. Number
5. String
6. Symbol (new in ECMAScript 6)
7. Object

关于typeof的详情解释

demo1：

Function.prototype.toString() 与 Object.prototype.toString()的区别：

var f = function(){};
f.prototype.hasOwnProperty("toString") ; //=>false
Function.prototype.hasOwnProperty("toString"); //=>true

Object.prototype.toString.call(f); //=>[object Function]

Function.prototype.toString(f);  //=>"function () {}"

Object.toString.call(f) ;  //=>"function () {}"

//注：Object 是由Function构造的，所以Object.toString会这样 ，由Object.__proto__.toString 遍历原型链去找到Function.prototype.toString() 打印，所以会打印function f(){}

//jquery 类型的判断，demo2
{}.toString.call(f);  //=>[object Function]

所以，所有由Object.prototype.toString 方法调用的对象，都是会打印出[object Function],[object String] 或者其他类似的格式，而这个结果也常常会被我们用来去判断这是否是一个String 字符串，Array ...

Object.prototype.toString.call([]) === "[object Array]"  // ==>"[object Array]"

Object.prototype.toString.call({}) === "[object Array]"  // ==>"[object Object]"

demo2:

jQuery.type() 方法的源码解析：

var class2type = {};

// Populate the class2type map
/* 覆盖class2type: 用做返回的的类型
  var class2type = {
    "[object Boolean]":"boolean",
    "[object Number]":"number",
    "[object String]":"string",
    "[object Function]":"function",
    "[object Array]":"array",
    "[object Date]":"date",
    "[object RegExp]":"regexp",
    "[object Object]":"object",
    "[object Error]":"error"
}
*/
jQuery.each( "Boolean Number String Function Array Date RegExp Object Error Symbol".split( " " ),
function( i, name ) {
	class2type[ "[object " + name + "]" ] = name.toLowerCase();
} );
    ...
    type: function( obj ) {
        //  return null
    	if ( obj == null ) {
    		return obj + "";
    	}

    	// Support: Android <=2.3 only (functionish RegExp)
    	// 支持: Android <= 2.3 版本  ?(functionish RegExp)
    	// 如果是个函数的话，返回class2type[{}.toString.call(obj)]
    	return typeof obj === "object" || typeof obj === "function" ?
    		class2type[ toString.call( obj ) ] || "object" :
    		typeof obj;
    },
    ...

On IE 6, 7, and 8 a lot of host objects are objects and not functions. For example: typeof alert === 'object'

This stnds since the beginning of JavaScript typeof null === 'object';

Regular expressions

在一些正则中，低版本的浏览器可能会不兼容es5

typeof /s/ === 'function'; // Chrome 1-12 不遵循  5.1
typeof /s/ === 'object';   // Firefox 5+  遵循 ECMAScript 5.1