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基本数据类型
| 数据类型 | 取值 |
| Undefined | undefined |
| Null | null |
| String | 凡是由引号包裹起来的数据 |
| Boolean | true/false |
| Number | 一切数字 |
通过typeof运算符可以判断出是哪种数据类型
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>变量的声明</title>
<script type="text/javascript">
var age =23;
age ="hello";
age="true";
alert(typeof age);
</script>
</head>
<body>
</body>
</html>
引用数据类型
1. Array
方法
- unshitf()
- shift()
- pop()
- push()
- sort()
- reverse()
String
- new String();
- String();
属性
- length
方法
- substring(stratIndex,endIndex)
- slice()
Boolean
- new Boolean();
- BOOLEAN();
Number
- new Number();
- Number();
Date
- new Date();
方法
- toLocationString()
Math
属性
- PI
方法
- random()
- round()
正则
/^$/
正则.test(需要匹配的值)
- 如果匹配：true
- 不匹配：false
全局函数
1.尝试转换
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>尝试转换</title>
<script type="text/javascript">
var s = "9.9超时";
var s_=parseInt(s);
alert(s_);
var s3 = parseFloat(s);
alert(s3);
</script>
</head>
<body>
</body>
</html>
2.强制转换
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>强制转换</title>
<script type="text/javascript">
var s1 = "9.9超时";
var s2 = Number(s1);//NaN
alert(s2);
</script>
</head>
<body>
</body>
</html>3.编码和解码
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>编码和解码</title>
<script type="text/javascript">
alert(decodeURI(location.href));
alert(encodeURI(decodeURI(location.href)));//编码的返回小
alert(encodeURIComponent(decodeURI(location.href)));//编码的返回更大
</script>
</head>
<body>
</body>
</html>
4.eval
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>eval</title>
<script type="text/javascript">
var s = "alert('1')";
// alert(s);
eval(s);
</script>
</head>
<body>
</body>
</html>