JavaScript数据类型转换
时间：2023-02-09 13:14:32 | 栏目：JavaScript代码 | 点击：次
一、转换函数
1、parseInt()
parseInt()函数可以将任何类型的值转换为整数。
例如：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>转换函数</title>
<script>
// parseInt()
var box="34";
alert(typeof parseInt(box)); // number
</script>
</head>
<body>
</body>
</html>
结果：
从上面的截图中可以看出：使用了parseInt()函数以后，box变成了整数。
注意：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>转换函数</title>
<script>
// parseInt()
/* var box="34";
alert(typeof parseInt(box)); // number */
var box="34sf3435"; //parseInt(box)=34
var box1="987.67";//parseInt(box1)=987
var box2="rr567";//parseInt(box2)=NaN
alert("box的值："+parseInt(box)+",box1的值:"+parseInt(box1)+",box2的值:"+parseInt(box2));
</script>
</head>
<body>
</body>
</html>
结果：
2、parseFloat()
parseFloat()转换函数可以将字符串转换为浮点数。
例如：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>转换函数</title>
<script>
// parseInt()
/* var box="34";
alert(typeof parseInt(box)); // number */
/* var box="34sf3435"; //parseInt(box)=34
var box1="987.67";//parseInt(box1)=987
var box2="rr567";//parseInt(box2)=NaN
alert("box的值："+parseInt(box)+",box1的值:"+parseInt(box1)+",box2的值:"+parseInt(box2)); */
// parseFloat()
var box="12.345";
var box1=parseFloat(box);
alert(typeof box1);//number
</script>
</head>
<body>
</body>
</html>
结果：
注意：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>转换函数</title>
<script>
// parseInt()
/* var box="34";
alert(typeof parseInt(box)); // number */
/* var box="34sf3435"; //parseInt(box)=34
var box1="987.67";//parseInt(box1)=987
var box2="rr567";//parseInt(box2)=NaN
alert("box的值："+parseInt(box)+",box1的值:"+parseInt(box1)+",box2的值:"+parseInt(box2)); */
// parseFloat()
/* var box="12.345";
var box1=parseFloat(box);
alert(typeof box1);//number */
var box="34.435"; //parseFloat(box)=34
var box1="987.67ererw";//parseFloat(box1)=987.67
var box2="rr567.12";//parseFloat(box2)=NaN
var box3="567wew.12";//parseFloat(box2)=NaN
alert("box的值："+parseFloat(box)+",box1的值:"+parseFloat(box1)+",box2的值:"+parseFloat(box2)+",box3的值:"+parseFloat(box3));
</script>
</head>
<body>
</body>
</html>
结果：
3、toString()
toString()转换函数返回字符串。
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>转换函数</title>
<script>
// parseInt()
/* var box="34";
alert(typeof parseInt(box)); // number */
/* var box="34sf3435"; //parseInt(box)=34
var box1="987.67";//parseInt(box1)=987
var box2="rr567";//parseInt(box2)=NaN
alert("box的值："+parseInt(box)+",box1的值:"+parseInt(box1)+",box2的值:"+parseInt(box2)); */
// parseFloat()
/* var box="12.345";
var box1=parseFloat(box);
alert(typeof box1);//number */
/* var box="34.435"; //parseFloat(box)=34
var box1="987.67ererw";//parseFloat(box1)=987.67
var box2="rr567.12";//parseFloat(box2)=NaN
var box3="567wew.12";//parseFloat(box2)=NaN
alert("box的值："+parseFloat(box)+",box1的值:"+parseFloat(box1)+",box2的值:"+parseFloat(box2)+",box3的值:"+parseFloat(box3)); */
// toString()
var a=4;
var b=7;
alert(a.toString()+b.toString());// 输出47，不是11
</script>
</head>
<body>
</body>
</html>
结果：
二、强制类型转换函数
1、Boolean()
Boolean()转换为Boolean值。
例如：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>转换函数</title>
<script>
// parseInt()
/* var box="34";
alert(typeof parseInt(box)); // number */
/* var box="34sf3435"; //parseInt(box)=34
var box1="987.67";//parseInt(box1)=987
var box2="rr567";//parseInt(box2)=NaN
alert("box的值："+parseInt(box)+",box1的值:"+parseInt(box1)+",box2的值:"+parseInt(box2)); */
// parseFloat()
/* var box="12.345";
var box1=parseFloat(box);
alert(typeof box1);//number */
/* var box="34.435"; //parseFloat(box)=34
var box1="987.67ererw";//parseFloat(box1)=987.67
var box2="rr567.12";//parseFloat(box2)=NaN
var box3="567wew.12";//parseFloat(box2)=NaN
alert("box的值："+parseFloat(box)+",box1的值:"+parseFloat(box1)+",box2的值:"+parseFloat(box2)+",box3的值:"+parseFloat(box3)); */
// toString()
/* var a=4;
var b=7;
alert(a.toString()+b.toString());// 输出47，不是11 */
// Boolean()
var a=8; //Boolean(a)：true 任何非0的数字都是true
var b=0; //Boolean(b)：false
var c="232"; // Boolean(c)：true 任何非空的字符串都是true
var d="";// Boolean(d)：false
var e; // Boolean(e)：false
var f=null; //Boolean(f)：false
document.write("a:"+Boolean(a)+"<br />");
document.write("b:"+Boolean(b)+"<br />");
document.write("c:"+Boolean(c)+"<br />");
document.write("d:"+Boolean(d)+"<br />");
document.write("e:"+Boolean(e)+"<br />");
document.write("f:"+Boolean(f)+"<br />");
</script>
</head>
<body>
</body>
</html>
结果：
2、Number()
Number()转换为数字。
例如：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>转换函数</title>
<script>
// parseInt()
/* var box="34";
alert(typeof parseInt(box)); // number */
/* var box="34sf3435"; //parseInt(box)=34
var box1="987.67";//parseInt(box1)=987
var box2="rr567";//parseInt(box2)=NaN
alert("box的值："+parseInt(box)+",box1的值:"+parseInt(box1)+",box2的值:"+parseInt(box2)); */
// parseFloat()
/* var box="12.345";
var box1=parseFloat(box);
alert(typeof box1);//number */
/* var box="34.435"; //parseFloat(box)=34
var box1="987.67ererw";//parseFloat(box1)=987.67
var box2="rr567.12";//parseFloat(box2)=NaN
var box3="567wew.12";//parseFloat(box2)=NaN
alert("box的值："+parseFloat(box)+",box1的值:"+parseFloat(box1)+",box2的值:"+parseFloat(box2)+",box3的值:"+parseFloat(box3)); */
// toString()
/* var a=4;
var b=7;
alert(a.toString()+b.toString());// 输出47，不是11 */
// Boolean()
/* var a=8; //Boolean(a)：true 任何非0的数字都是true
var b=0; //Boolean(b)：false
var c="232"; // Boolean(c)：true 任何非空的字符串都是true
var d="";// Boolean(d)：false
var e; // Boolean(e)：false
var f=null; //Boolean(f)：false
document.write("a:"+Boolean(a)+"<br />");
document.write("b:"+Boolean(b)+"<br />");
document.write("c:"+Boolean(c)+"<br />");
document.write("d:"+Boolean(d)+"<br />");
document.write("e:"+Boolean(e)+"<br />");
document.write("f:"+Boolean(f)+"<br />"); */
// Number()
var a="34"; //Number(a)：34
var b="67.34";//Number(b)：67.34
var c="45ttt";//Number(c)：NaN
var d="";//Number(d)：0
var e=true;//Number(a)：1
var f=false;//Number(a)：0
var g;//Number(a)：NaN
var h=null;//Number(a)：0
document.write("a:"+Number(a)+"<br />");
document.write("b:"+Number(b)+"<br />");
document.write("c:"+Number(c)+"<br />");
document.write("d:"+Number(d)+"<br />");
document.write("e:"+Number(e)+"<br />");
document.write("f:"+Number(f)+"<br />");
document.write("g:"+Number(g)+"<br />");
document.write("h:"+Number(h)+"<br />");
</script>
</head>
<body>
</body>
</html>
结果：
3、String()
String()转换为字符串。
例如：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>转换函数</title>
<script>
// parseInt()
/* var box="34";
alert(typeof parseInt(box)); // number */
/* var box="34sf3435"; //parseInt(box)=34
var box1="987.67";//parseInt(box1)=987
var box2="rr567";//parseInt(box2)=NaN
alert("box的值："+parseInt(box)+",box1的值:"+parseInt(box1)+",box2的值:"+parseInt(box2)); */
// parseFloat()
/* var box="12.345";
var box1=parseFloat(box);
alert(typeof box1);//number */
/* var box="34.435"; //parseFloat(box)=34
var box1="987.67ererw";//parseFloat(box1)=987.67
var box2="rr567.12";//parseFloat(box2)=NaN
var box3="567wew.12";//parseFloat(box2)=NaN
alert("box的值："+parseFloat(box)+",box1的值:"+parseFloat(box1)+",box2的值:"+parseFloat(box2)+",box3的值:"+parseFloat(box3)); */
// toString()
/* var a=4;
var b=7;
alert(a.toString()+b.toString());// 输出47，不是11 */
// Boolean()
/* var a=8; //Boolean(a)：true 任何非0的数字都是true
var b=0; //Boolean(b)：false
var c="232"; // Boolean(c)：true 任何非空的字符串都是true
var d="";// Boolean(d)：false
var e; // Boolean(e)：false
var f=null; //Boolean(f)：false
document.write("a:"+Boolean(a)+"<br />");
document.write("b:"+Boolean(b)+"<br />");
document.write("c:"+Boolean(c)+"<br />");
document.write("d:"+Boolean(d)+"<br />");
document.write("e:"+Boolean(e)+"<br />");
document.write("f:"+Boolean(f)+"<br />"); */
// Number()
/* var a="34"; //Number(a)：34
var b="67.34";//Number(b)：67.34
var c="45ttt";//Number(c)：NaN
var d="";//Number(d)：0
var e=true;//Number(e)：1
var f=false;//Number(f)：0
var g;//Number(g)：NaN
var h=null;//Number(h)：0
document.write("a:"+Number(a)+"<br />");
document.write("b:"+Number(b)+"<br />");
document.write("c:"+Number(c)+"<br />");
document.write("d:"+Number(d)+"<br />");
document.write("e:"+Number(e)+"<br />");
document.write("f:"+Number(f)+"<br />");
document.write("g:"+Number(g)+"<br />");
document.write("h:"+Number(h)+"<br />"); */
// String()
var a=34; //String(a)：34
var b=67.34;//String(b)：67.34
var c=true;//String(c)：true
var d=false;//String(d)：false
var e=null;//String(e)：null
var f; //String(f):undefined
document.write("a:"+String(a)+"<br />");
document.write("b:"+String(b)+"<br />");
document.write("c:"+String(c)+"<br />");
document.write("d:"+String(d)+"<br />");
document.write("e:"+String(e)+"<br />");
document.write("f:"+String(f)+"<br />");
</script>
</head>
<body>
</body>
</html>
结果：
