Home Web Front-end JS Tutorial Introduction and application of regular metacharacters

Introduction and application of regular metacharacters

Jul 02, 2017 am 09:27 AM
javascript Summarize

1. Metacharacters:

Each regular expression is composed of metacharacters and modifiers

[Metacharacters] ->Some characters with special meaning between two /

reg = /^\d$/  //只能是一个0-9之间的数字
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 1. Characters with special meaning Metacharacter

## \: Escape character, translate the meaning of the following characters

 ^: Start with a certain metacharacter

 $: ends with a metacharacter 

\n: matches a newline character

 .: Any character except \n 

 (): Grouping-> Divide a large regular pattern into several small regular patterns  

 x|y: One of x or y

 [xyz]: One of x, y or z A

## [^xyz]: Any character except three

 [a-z]: Any character between a-z

 [^a-z]: Except any character between a-z

 \d: A character between 0-9 \D Any characters except numbers between 0-9

## \b: A boundary character "w1 w2 w3"

##\w: Any character among numbers, letters, and underscores [0-9a-zA-Z_]

##\s: Matches a whitespace character, a space, a tab character, a form feed character.. .

## 2. Quantifier metacharacter representing the number of occurrences

 *: Appear zero to multiple times

  + : Appears 1 or more times

 ? :Occurs zero or 1 times

 {n} :Occurs n times

 {n,} :Occurs n to multiple times

 {n,m}: appears n to m times

 

 reg = /^\d+wo\d+$/;  reg = /^(\d+)wo(\d+)$/;
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var reg = /^0.2$/   // 以0开头 2结尾,中间可以是除了\n的任意字符
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var reg = /^\d+$/;//只能是多个数字console.log(reg.test('2017'))//true//一个简单的验证手机号的正则:11位数字,第一位为1var reg = /^1\d{10}$/;
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2. Application of metacharacters
 []

  1. All characters appearing in square brackets The characters are all characters that represent their own meaning (no special meaning).

 2. Square brackets do not recognize two digits

 

var reg = /^[12-68]$/ -> ;Represents one of 1, 2-6, and one of 8. This method is wrong

 ()

1. Function 1 of grouping: Change the default priority of x|y

       var reg = /^18|19$/;//符合条件的有18、19、181、189、119、819、1819
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       var reg = /^(18|19)$/  //18、19
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 1. Regular rules for valid numbers: positive numbers, negative numbers, zero, decimals
## 1), "." may or may not appear, but once it appears, it must be followed by Followed by one or more digits

  2), there may be +/- at the beginning or not

  3), the integer part, A single digit can be one between 0-9, and multiple digits cannot start with 0

 The regular rules are as follows

 

var reg = /^[+-]?(\d|([1-9]\d+))(\.\d+)?$/
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