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类型检测小结:
typeof:适合基本类型及function检测，遇到null失效。
[[Class]]:通过{}.toString拿到，适合内置对象和基元类型，遇到null和undefined失效（IE678等返回[object Object]）.
instanceof:适合自定义对象，也可以用来检测原生对象，在不同iframe和window间检测时失效。
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html;charset=UTF-8">
<title>Document</title>
<script type="text/javascript">
// var a = [10,1,2,3,4,8,9];
// function max(a){
// var len = a.length-1;
// alert(a.length-1)
// var maxnum=a[len];
// while (len--) {
// maxnum=Math.max(maxnum,a[len])
// }
// return maxnum;
// }
// alert(max(a));
var num =32;
num="this is a string"
console.log(32+32);//64
console.log("32"+32);//3232
console.log("32"-32);//0
var x=‘the answer is‘+42;
var y=42+‘is the answer‘;
console.log(x);//the answer is42
console.log(y);//42is the answer
console.log("37"-7);//30
console.log("37"+7)//377
console.log(null-0);//0
console.log(null);//null
//巧用+/—规则转换类型:num-0变量null转为数字；数字变成字符串num+"".
//等和严格等：
console.log("1.23"==1.23);//true
console.log(0==false);//true
console.log(null==undefined);//true
console.log(new Object()==new Object());//false
console.log([1,2]==[1,2])//false
//console.log(a===b);
//严格等，等号两边的类型：
console.log(null===null);//true
console.log(undefined===undefined);//true
console.log(NaN===NaN);//false
console.log(new Object()===new Object());//false
//不严格等：类型相同，同===；类型不同，尝试类型转换和比较
console.log(null==undefined);//ture
//console.log(number==string);
console.log(1=="1.0");//true
//console.log(boolean==number);
console.log(1==true);//true
//console.log(object==number|string);
console.log(new String(‘hi‘)==‘hi‘)//true
// var str="string"//undefined
// var strObj=new String("string")//undefined
// str//"string"//0"s",1 "t",2 "r",3"i",4"n",5"g".
// str//"string"
// str.length//6
// str.t=10//10
// str.t//undefind
// str.t=3//3
// var number=123//undefined
// var numObj=new Number("number")//undefined
// number.length//undefined
// number+number//246
// number+""//"123"
//类型检测
//基本类型 函数对象typeof
console.log(typeof 100)//number
console.log(typeof true)//boolean
console.log(typeof function(){})//function
console.log(typeof(undefined))//undefined
console.log(typeof new Object())//object
console.log(typeof [1,2])//array
console.log(typeof NaN)//number*
console.log(typeof null)//object*
//obj instanceof Object
console.log([1,2] instanceof Array)//true
console.log(new Object() instanceof Array)//false
console.log()
console.log()
//Object.prototype.toString
console.log(Object.prototype.toString.apply([1,2,3]))//[object Array]
console.log(Object.prototype.toString.apply(function(){
var a=1,b=2,c;
return c=a+b;
}))//[object Function]
console.log(Object.prototype.toString.apply(null))//[object Null]
console.log(Object.prototype.toString.apply(undefined))//[object Undefined]
</script>
</head>
<body>
</body>
</html>
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原文地址：http://www.cnblogs.com/xl900912/p/4218293.html
