number,string,boolean
强制转换
string,boolean—>number Number(value)
string—>number 只能识别纯数字的字符串 

  1. <!DOCTYPE html>
  2. <html lang="en">
  3. <head>
  4.     <meta charset="UTF-8">
  5.     <meta name="viewport" content="width=device-width, initial-scale=1.0">
  6.     <title>Document</title>
  7. </head>
  8. <body>
  9.     <script>
  10.         // number,string,boolean
  11.         // 强制转换
  12.         // string,boolean-->number Number(value)
  13.         /* string-->number 只能识别纯数字的字符串 */
  14.         var str = "10";
  15.         var s = "hello world";
  16.         var t = "2121fsf";
  17.         var num = Number(str);
  18.         console.log(num);
  19.         console.log(Number(s)); //NaN 不是一个数字
  20.         console.log(Number(t));
  21.     </script>
  22. </body>
  23. </html>

number，string转boolean

number,string—> Boolean(value)
特殊:0—>false;

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        //特殊：0-->false；
        //特殊：""-->false；
        var a = 0;
        var b = -1;
        var c = 10;
        var d = "hello world";
        var e = " ";
        var f = "";
        console.log(Boolean(a));
        console.log(Boolean(b));
        console.log(Boolean(c));
        console.log(Boolean(d));
        console.log(Boolean(e));
        console.log(Boolean(f));
    </script>
</body>
</html>

Boolean-number

boolean—>number
true—>1
false —>0

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        var b =true;
        var f =false;
        console.log(Number(b));
        console.log(Number(f));
    </script>
</body>
</html>