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）有：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：
1、typeof
可以识别标准类型（Null除外）
不能识别对象类型（Function除外）
2、Prototype.toString()
可以识别标准类型
可以识别对象类型
不能识别自定义对象类型
3、constructor
可以识别标准类型（undefined Null除外）
可以识别对象类型
可以识别自定义对象类型
4、instanceof
不能识别标准类型
可以识别对象类型
可以识别自定义对象类型
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。
时间： 2024-10-07 09:09:14