定义：规定字符串中字符出现规律的表达式

1.正则的语法

备选字符集: [海天] 特点:多选一
定义:规定某一位字符的备选字符列表

  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.         // 备选字符集:  [海天]  特点:多选一
  11.         /* 定义:规定某一位字符的备选字符列表 */
  12.         var str = "上海,上天,上哪里去";  //"*"
  13.         var reg = /上[海天]/g
  14.         console.log(str.replace(reg,"*"))//*,*,上哪里去
  15.     </script>
  16. </body>

2.reg

正则表达式 规则表达
正则的语法 /keyword/
i忽略大小写 g全局替换

<!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 str = "hellLo";
        // 正则表达式   规则表达
        var reg = /l/ig;
        // 正则的语法  /keyword/
        // ig   i忽略大小写   g全局替换
        console.log(str.replace(reg,"*"));// "he***o";
    </script>
</body>
</html>


<!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 str ="美国&nbsp;"
        var reg = /&nbsp;/g;
        console.log(str.replace(reg,""))
    </script>
</body>
</html>

<!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 str = "<span>2201239人评价</span>";
        //2201239
        var reg = /[^\d]/g;
        console.log(str.replace(reg,""))
    </script>
</body>
</html>

3.反选选择

var reg = /[^0-9]/g;

<!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 str = "fdsfds12121dsf";
        /*  */
        var reg = /[^0-9]/g;
        console.log(str.replace(reg,""));//12121
    </script>
</body>
</html>

4.reg.test(str)

规则字符串中字符出现规律的表达式

<!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>
        // 规则字符串中字符出现规律的表达式
        /*  reg.test(str) */
        var str  = "hello";
        var reg  =/l/g;
        console.log(str.replace(reg,"*"));
        console.log(reg.test(str))
    </script>
</body>
</html>

5.我们写的正则表达式，只要符合字符串的某一段就可以了

<!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>
        /*
        正则：
        我们写的正则表达式，只要符合字符串的某一段就可以了
        */
        var str = "abc1234556777";
        var reg = /\d{3,5}/;
        console.log(reg.test(str))
    </script>
</body>
</html>