JavaScript变量命名与类型转换实战指南-优快云博客

本文链接：https://blog.youkuaiyun.com/LYN_1217/article/details/125172130

一、 js变量命名规则：
由字母、数字、下划线、$组成
不以数字开头
不能是关键字或保留字

二、其他类型转换为字符串string
1、+""拼接

<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
	</head>
	<body>
		<script>
			// 1.+""拼接
			console.log(typeof(3 + "")); //string
			console.log(3 + "2"); //32
			console.log("3+2"); //3+2
		</script>
	</body>
</html>

2、String(),首字母必须大写

<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
	</head>
	<body>
		<script>
				// 2.String(),首字母必须大写
				var a=String(3);
				var b=String(true);
				var c=String(null);
				console.log(typeof(a));	//string
				console.log(typeof(b));	//string
				console.log(typeof(c));	//string
				console.log(b);		//"true"
				console.log(c);		//"null"
		</script>
	</body>
</html>

三、其他类型转换为数值
1、*1

<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
	</head>
	<body>
		<script>
			//1、*1
			console.log(typeof("2"*1));			//number
			console.log("2"*1);					//2
			console.log(typeof(true*1));		//number
			console.log(false*1);				//0
			console.log(typeof("ab"*1));		//number
			
			//NaN:not a number,不是相应数值
			console.log("ab"*1);				//NaN
			console.log(undefined*1);			//NaN
			
		</script>
	</body>
</html>

2、Number

<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
	</head>
	<body>
		<script>
			//2、Number
			console.log(typeof(Number("2")));	//number
			console.log(Number(true));			//1
			console.log(Number("aa"));			//NaN
			console.log(Number("11aa"));		//NaN
		</script>
	</body>
</html>

3、parseInt 整形，不是四舍五入，截取前面整数

<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
	</head>
	<body>
		<script>
			//3、parseInt 整形，不是四舍五入，截取前面整数
			console.log(parseInt("11.76"));		//11
			console.log(parseInt("11aa"));		//11
			console.log(parseInt("aa11"));		//NaN
			console.log(parseInt("1a1a"));		//1
		</script>
	</body>
</html>

4、parseFloat 浮点型

<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
	</head>
	<body>
		<script>
			//4、parseFloat 浮点型
			console.log(parseFloat("11.76"));	//11.76
			console.log(parseFloat("11.76a"));	//11.76
		</script>
	</body>
</html>

四、其他类型转换为布尔类型
1、前边加!!

<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
	</head>
	<body>
		<script>
			//1、前边加!!
			console.log(!!"aa");				//true
			console.log(!!"");					//false
			console.log(!!"true");				//true
			console.log(!!null);				//false
			console.log(!!undefined);			//false
			console.log(!!1);					//true
			console.log(!!0);					//false
		</script>
	</body>
</html>

2、Boolean

<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
	</head>
	<body>
		<script>
			//2、Boolean
			console.log(Boolean("aa"));			//true
			console.log(Boolean(""));			//false
			console.log(Boolean("true"));		//true
			console.log(Boolean(1));			//true
		</script>
	</body>
</html>

js的其他类型转换