类型判断
类型识别
typeofObject.prototype.toStringconstructorinstanceof
typeof：
- 可以是标准类型（Null 除外）
- 不可识别具体的对象类型（Function 除外）
Object.prototype.toString：
- 可是识别标准类型及内置对象类型（例如，Object, Date, Array）
- 不能识别自定义对象类型
constructor：
- 可以识别标准类型（Undefined/Null 除外）
- 可识别内置对象类型
- 可识别自定义对象类型
function getConstructiorName(obj) {
return obj && obj.constructor && obj.constructor.toString().match(/function\s*([^(]*)/)[1];
}
getConstructiorName([]) === "Array"; // true
instanceof：
- 不可判别原始类型
- 可判别内置对象类型
- 可判别自定义对象类型
JavaScript的数据类型可以分为：标准类型和对象类型。
标准类型有：undefined Null Boolean Date Number Object
对象类型（构造器类型）：Boolean Date Number Object Array Date Error Function RegExp
用来判断数据类型的一般有四种方式，分别是：
typeofPrototype.toString()constructorinstanceof
下面我们写一个HTML来检验一下：
<html>
<head>
<title>JavaScript类型判断</title>
<meta charset="utf-8">
<style type="text/css">
.red{
background-color:red;
}
</style>
</head>
<body>
<script type="text/javascript">
/* Standard Type */
var a; //undefined
var b = document.getElementById("no_exist_element"); //null
var c = true; //Boolean
var d = 1; //Number
var e = "str"; //String
var f = {name : "Tom"}; //Object
/* Object Type */
var g = new Boolean(true); //Boolean Object
var h = new Number(1); //Number Object
var i = new String("str"); //String Object
var j = new Object({name : "Tom"}); //Object Object
var k = new Array([1, 2, 3, 4]); //Array Object
var l = new Date(); //Date Object
var m = new Error();
var n = new Function();
var o = new RegExp("\\d");
/* Self-Defined Object Type */
function Point(x, y) {
this.x = x;
this.y = y;
}
Point.prototype.move = function(x, y) {
this.x += x;
this.y += y;
}
var p = new Point(1, 2);
/* Use the Prototype.toString() to judge the type */
function type(obj){
return Object.prototype.toString.call(obj).slice(8, -1).toLowerCase();
}
</script>
<table border="1" cellspacing="0">
<tr>
<td></td>
<td>typeof</td>
<td>toString</td>
<td>constructor</td>
<td>instanceof</td>
</tr>
<tr>
<td>undefined</td>
<td><script type="text/javascript">document.write(typeof a)</script></td>
<td><script type="text/javascript">document.write(type(a))</script></td>
<td class="red"><script type="text/javascript">document.write(a.constructor)</script></td>
<td class="red"><script type="text/javascript">document.write(a instanceof "undefined")</script></td>
</tr>
<tr>
<td>Null</td>
<td class="red"><script type="text/javascript">document.write(typeof b);</script></td>
<td><script type="text/javascript">document.write(type(b));</script></td>
<td class="red"><script type="text/javascript">document.write(b.constructor);</script></td>
<td class="red"><script type="text/javascript">document.write(b instanceof "null");</script></td>
</tr>
<tr>
<td>Boolean</td>
<td><script type="text/javascript">document.write(typeof c);</script></td>
<td><script type="text/javascript">document.write(type(c));</script></td>
<td><script type="text/javascript">document.write(c.constructor);</script></td>
<td class="red"><script type="text/javascript">document.write(c instanceof "boolean");</script></td>
</tr>
<tr>
<td>Number</td>
<td><script type="text/javascript">document.write(typeof d);</script></td>
<td><script type="text/javascript">document.write(type(d));</script></td>
<td><script type="text/javascript">document.write(d.constructor);</script></td>
<td class="red"><script type="text/javascript">document.write(d instanceof "number");</script></td>
</tr>
<tr>
<td>String</td>
<td><script type="text/javascript">document.write(typeof e);</script></td>
<td><script type="text/javascript">document.write(type(e));</script></td>
<td><script type="text/javascript">document.write(e.constructor);</script></td>
<td class="red"><script type="text/javascript">document.write(e instanceof "string");</script></td>
</tr>
<tr>
<td>Object</td>
<td><script type="text/javascript">document.write(typeof f);</script></td>
<td><script type="text/javascript">document.write(type(f));</script></td>
<td><script type="text/javascript">document.write(f.constructor);</script></td>
<td class="red"><script type="text/javascript">document.write(f instanceof "object");</script></td>
</tr>
<tr><td colspan="5">-----------------------</td></tr>
<tr>
<td>Boolean Object</td>
<td class="red"><script type="text/javascript">document.write(typeof g);</script></td>
<td><script type="text/javascript">document.write(type(g));</script></td>
<td><script type="text/javascript">document.write(g.constructor);</script></td>
<td><script type="text/javascript">document.write(g instanceof Boolean);</script></td>
</tr>
<tr>
<td>Number Object</td>
<td class="red"><script type="text/javascript">document.write(typeof h);</script></td>
<td><script type="text/javascript">document.write(type(h));</script></td>
<td><script type="text/javascript">document.write(h.constructor);</script></td>
<td><script type="text/javascript">document.write(h instanceof Number);</script></td>
</tr>
<tr>
<td>String Object</td>
<td class="red"><script type="text/javascript">document.write(typeof i);</script></td>
<td><script type="text/javascript">document.write(type(i));</script></td>
<td><script type="text/javascript">document.write(i.constructor);</script></td>
<td><script type="text/javascript">document.write(i instanceof String);</script></td>
</tr>
<tr>
<td>Object Object</td>
<td class="red"><script type="text/javascript">document.write(typeof j);</script></td>
<td><script type="text/javascript">document.write(type(j));</script></td>
<td><script type="text/javascript">document.write(j.constructor);</script></td>
<td><script type="text/javascript">document.write(j instanceof Object);</script></td>
</tr>
<tr>
<td>Array Object</td>
<td class="red"><script type="text/javascript">document.write(typeof k);</script></td>
<td><script type="text/javascript">document.write(type(k));</script></td>
<td><script type="text/javascript">document.write(k.constructor);</script></td>
<td><script type="text/javascript">document.write(k instanceof Array);</script></td>
</tr>
<tr>
<td>Date Object</td>
<td class="red"><script type="text/javascript">document.write(typeof l);</script></td>
<td><script type="text/javascript">document.write(type(l));</script></td>
<td><script type="text/javascript">document.write(l.constructor);</script></td>
<td><script type="text/javascript">document.write(l instanceof Date);</script></td>
</tr>
<tr>
<td>Error Object</td>
<td class="red"><script type="text/javascript">document.write(typeof m);</script></td>
<td><script type="text/javascript">document.write(type(m));</script></td>
<td><script type="text/javascript">document.write(m.constructor);</script></td>
<td><script type="text/javascript">document.write(m instanceof Error);</script></td>
</tr>
<tr>
<td>Function Object</td>
<td><script type="text/javascript">document.write(typeof n);</script></td>
<td><script type="text/javascript">document.write(type(n));</script></td>
<td><script type="text/javascript">document.write(n.constructor);</script></td>
<td><script type="text/javascript">document.write(n instanceof Function);</script></td>
</tr>
<tr>
<td>RegExp Object</td>
<td class="red"><script type="text/javascript">document.write(typeof o);</script></td>
<td><script type="text/javascript">document.write(type(o));</script></td>
<td><script type="text/javascript">document.write(o.constructor);</script></td>
<td><script type="text/javascript">document.write(o instanceof RegExp);</script></td>
</tr>
<tr><td colspan="5">-----------------------</td></tr>
<tr>
<td>Point Objct</td>
<td class="red"><script type="text/javascript">document.write(typeof p);</script></td>
<td class="red"><script type="text/javascript">document.write(type(p));</script></td>
<td><script type="text/javascript">document.write(p.constructor);</script></td>
<td><script type="text/javascript">document.write(p instanceof Point);</script></td>
</tr>
</table>
</body>
</html>
执行的结果如下：
其中红色的单元格表示该判断方式不支持的类型。