ES6 |正则表达式

RegEx是正则表达式的缩写形式，它是定义模式的字符序列。 RegEx 中的字符可以是字母、数字或特殊字符。通常，RegEx 用于在字符串中查找模式以替换、删除或修改它们。在 ES6 中，RegEx 可以由 2 种不同的符号定义。

• 字面量表示法：模式用斜线括起来。它在编译时执行。因此，常量模式可以用字面量表示法给出。

  var regex = /pattern/

• 构造函数：模式在单引号内给出。它在运行时执行。因此，可以在构造函数中给出灵活的模式。

  var regex = new RegExp( pattern, optional arguments)

下面列出了提及模式的不同方式：

方括号的使用：它用于提及模式中特定范围的字符。

Patterns with brackets	Description
[pattern]	Any one character from the pattern.
[^pattern]	Any one character not from the pattern.
[0-9]	Any one decimal number between 0-9.
[a-z]	Any one character from the lower case alphabets.
[A-Z]	Any one character from the upper case alphabets.

量词的使用：用于指定字符在模式中出现的频率和位置。

Quantifiers	Description
pattern+	Matches strings with atleast one or more pattern.
pattern*	Matches strings with zero or more patterns.
pattern{n}	Matches strings with ‘n’ number of patterns.
pattern{n1, n2}	Matches strings with patterns in range from n1 to n2 (Both inclusive).
pattern{n, }	Matches strings with minimum ‘n’ number of patterns.
pattern$	Matches strings with pattern as the end sequence.
^pattern	Matches strings with pattern as the beginning sequence.

字面量字符的使用：用于指定转义字符。

Literal Characters	Description
\0	It denotes a NULL character.
\t	It denotes a tab space.
\n	It denotes a newline.
\r	It denotes a carriage return.

元字符的使用：仅用于指定字符的类型。

Meta Characters	Description
\s	It denotes a blank or whitespace.
\S	It denotes a non-blank or no space character.
\d	It denotes a decimal digit character.
\D	It denotes a non-digit character.
\w	It denotes a word character (Any character sequence).
\W	It denotes a non-word character.

例子：

    var text1 = "Welcome to GeeksforGeeks ";
  
    var text2 = "The numbers are - 0, 1, 2, "
              + "3, 4, 5, 6, 7, 8, 9. The "
              + "special characters are - @,"
              + " #, $, %, ^, &, *";
  
    // RegExp.match() and RegExp.replace()
    // have been used in the following
    // examples
  
    // Bracket notations
    // 1
    var regexp = new RegExp('[geeks]');
    console.log(text1.match(regexp));
      
    // 2
    var regexp = new RegExp('[^geeks]');
    console.log(text1.match(regexp));
      
    // 3
    var regexp = new RegExp('[0-9]');
    console.log(text2.match(regexp));
  
    // Quantifiers
    // 4
    var regexp = new RegExp('[geeks]*');
    console.log(text1.match(regexp));
      
    // 5
    var regexp = new RegExp('s{2}');
    console.log(text1.match(regexp));
  
    // Literal characters and meta characters
    // 6
    var regexp1 = /(\w+)\s(\w+)\s(\w+)/
    let newtext = text1.replace(regexp1, '$3 $2 $1');
    console.log(newtext);
  
    // 7
    var regexp1 = /(\d+)/;
    let newtext1 = text2.replace(regexp1, 'number');
    console.log(newtext1);
  
    // 8
    var regexp2 = /(\s+)/;
    console.log(text2.replace(regexp2, '\t'));

输出：

注意： RexExp 本身没有方法和属性。但是它从原型中继承了一些功能和属性。