JS foundation -- regular expression

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One 、 What is regular expression ？

Regular expressions are sequences of characters that make up a search pattern .
When searching for data in text , Search patterns can be used to describe the content of the search .
Regular expressions can be single characters , Or more complex patterns .
Regular expressions can be used to perform all types of text search and text substitution operations .
for example ：
/Ljy/i Is a regular expression .
Ljy Is the mode （ Use... In search ）.
i It's a modifier （ Change the search to case insensitive ）.

Two 、 Regular expression modifiers

Modifier	describe
i	Perform a match that is not case sensitive .
g	Perform a global match （ Find all matches instead of stopping after finding the first one ）.
m	Perform multi line matching .

3、 ... and 、 Regular expression patterns

Parentheses are used to find a range of strings ：

expression	describe
[abc]	Look for any characters between brackets .
[0-9]	Find anything from 0 to 9 The number of .
(x|y)	Look up the information from

Metacharacters are characters with special meanings ：

Metacharacters	describe
\d	Find number .
\s	Look for blank characters .
\b	Match word boundaries .
\uxxxx	Find in hexadecimal numbers xxxx Stipulated Unicode character .

Quantifiers Define quantifiers ：

quantifiers	describe
n+	Match any containing at least one n String .
n*	Match any containing zero or more n String .
n?	Match any containing zero or one n String .

Four 、 How to use regular expressions ？

Methods in strings

search()

search() Method uses an expression to search for a match , Then return to the matching position .

            var str = "ljy666";
			console.log(str.search(/666/g))

z

replace()

replace() Method returns the modified string where the pattern is replaced .

            var str = "ljy666";
			console.log(str.replace(/666/g,999))

match

match() Method to retrieve the specified value in a string , Or find a match for one or more regular expressions .
Return value : An array of matching results . The contents of the array depend on regexp Is there a global flag g.

            var str = "ljy666j88j";
			var reg=/j/g
			console.log(str.match(reg))

split

split() Method is used to split a string into an array of strings . If the regular expression passed in , Then it is divided according to the character matched by the regular expression .

            var str = "ljy666j88j";
			var reg=/[6-8]/g
			console.log(str.split(reg))

Regular expression methods

test()

It searches for strings through patterns , And then, based on the results, it returns true or false.

            var str = "ljy666";
			var reg=/j/g
			console.log(reg.test(str))

exec()

It's through a specified pattern （pattern） Search string , And return the found text .
If no match is found , Then return to null.

            var str = "ljy666";
			var reg=/j/g
			console.log(reg.exec(str))

5、 ... and 、 Case study

1. Determine whether the file is JPG perhaps PNG picture .jpg perhaps .png ending

			var reg=/\.(jpg|png)$/ //.jpg  perhaps  .png ending 
			var str="ljy.js"
			var re=reg.test(str)
			console.log(re)

2. Remove the leading and trailing spaces of the string

			var reg=/^\s/g
			var str="  ab c "
			var re=str.replace(reg,"")	
			console.log("---"+re+"--")	

3. Determine whether it is a mobile phone number

           var reg=/^1[3|5|6|7|8|9][0-9]{9}/
		   var str=18888888888
		   console.log(reg.test(str))