<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>测试Javascript</title>
</head>
<body>
<form>
<input x-webkit-speech lang="zh" x-webkit-grammer="bUIltin:search">
</form>
<script type="text/javascript">
//一、数据类型自动转换
var a = 5, b = 7;
document.write(a + b + '<br>'); //数值相机 12
document.write(a + '' + b + '<br>'); //数值转字符串相加 57
var s = '5';
document.write(a + s + '<br>'); //数值与字符串相加 55
document.write(a + (s - 0) + '<br>');//字符串转数值相加 10
document.write(!!a + '<br>');//数值转布尔值 true
document.write(!!a + !b + '<br>');//数值转布尔值再转数值相加 1
document.write((null == undefined) + '<br>'); //null 和 undefined互相比较 true
document.write((a == s) + '<br>'); //字符串数值比较true
document.write(a === s);//不转换，用 === 严格比较 false
//二、数据类型强制转换
var a = 110, b = '50', c = 40, d = '123.95';
var c1 = a + b; // 自动转换 "11050"
var c2 = a - b; // 自动转换 50
var c3 = a + parseInt(b); //b强制转换为整形 160
var c4 = a.toString() + c.toString(); //a、c均转换为字符串， 11040
var c5 = a + parseFloat(d); //c 强制转换成浮点型， 233.95
document.write(" c1=" + c1 + " c2=" + c2 + " c3=" + c3 + " c4=" + c4 + " c5=" + c5 + " <br>");
//三、通过构造函数进行强制类型转换
function dwn(s)
{
document.write(s + '<br>');
}
//字符串类型的强制转换
var str = '100';
var num = Number(str); //强制转换为Number
dwn(typeof(num) + ':' + num);
var obj = Object(str); // 强制转换为object
dwn(typeof(obj) + ':' + obj);
var bool = Boolean(str); //强制转换为 boolean
dwn(typeof(bool) + ':' + bool);
var fun = Function(str); //强制转化为 function
dwn(typeof(fun) + ':' + fun);
//数值类型的强制转换
var num = 100;
var str = String(num); //强制转换为String
dwn(typeof(str) + ':' + str);
var obj = Object(num); // 强制转换为object
dwn(typeof(obj) + ':' + obj);
var bool = Boolean(num); //强制转换为 boolean
dwn(typeof(bool) + ':' + bool);
//布尔类型的强制转换
var bool = 100;
var str = String(bool); //强制转换为String
dwn(typeof(str) + ':' + str);
var obj = Object(bool); // 强制转换为object
dwn(typeof(obj) + ':' + obj);
var num = Number(bool); //强制转换为 number
dwn(typeof(num) + ':' + num);
//对象类型的强制转换
var obj = {};
var str = String(obj); //强制转换为String
dwn(typeof(str) + ':' + str);
var bool = Boolean(obj); //强制转换为 boolean
dwn(typeof(bool) + ':' + bool);
var num = Number(obj); //强制转化为 number
dwn(typeof(num) + ':' + num);
</script>
</body>
</html>
