regular expression

Regular expressions （Regular Expression）

​ 1） Regular creation

​ 2） Regular matching method

​ 3） Metacharacters

​ 4） Character set

​ 5） The border

​ 6） grouping

 7） backreferences 

​ 8） Quantitative vocabulary

​ 9） Matching mode

//  Regular expressions ;["12312","2312"]
//  Find the corresponding number in the string ;
 Regular implementation ; +  appear 1 Times to times ; \d; Numbers ;\D: The digital ;
let reg = /\d+/g;
let arr = str.match(reg);
console.log(arr);

---

Knowledge point

### String manipulation

• Find the number in the string ;
• How to implement regularization

Regular creation

• Literal creation
• By constructor

//  Regular create ;
//  Mode one : Literal creation ;
let str = "fdsadf12313fdaf";
let a = "ad";
let reg = /a/;
let res = str.match(reg);
console.log(res);

//  Creation mode 2  ： Constructor creation ;
// let str = "fdsadf12313fdaf";
// let a = "ad";
// let reg = new RegExp(a,"g");
// let res = str.match(reg);
// console.log(res);

Regular matching method

String method

• match
• search
• replace
• split

1.split
let str = "fdafdafdsfdsafsddarer";
let arr = str.split(/a/);
console.log(arr);

//2.replace;
let str = "fdafdaf1dsfdsa2fsdda33rer";
let reg = /\d+/g;
let res = str.replace(reg,"*");
console.log(res);   fdafdaf*dsfdsa*fsdda*rer
//  Sensitive word filtering ;
let str = " According to the data of China's Ministry of Education ,2007 - 2018 year , The number of Chinese studying abroad is from 14 Ten thousand to 66.2 ten thousand , The average annual growth is about 14%; The number of returned students in the same period increased from 4 Ten thousand to 51.9 ten thousand , Average annual growth of nearly 24%. Under the rush of returning home , How about the supply and demand market for returnees , Become the common concern of overseas students and domestic employers .";
//  The Ministry of Education  、  personnel ;
let reg = / The Ministry of Education | personnel /g;
// let res = str.replace(reg,"*");
let res = str.replace(reg,function(arg){
    
    return "*".repeat(arg.length);
})
console.log(res);

// 3.match;
let str = "fdsa1231dfaf232fda";
let reg = /\d+/g;
let res =  str.match(reg);
console.log(res);
//  matching  //  Content between 
let str = /official/bannerManage  
let reg = /\/([\s\S]*?)\//
str = str.match(reg)[1]
console.log(str, ' result ')//official

// 4.search: Match the position of the first index value that matches the result ; If you can't find it   Just return it -1;
//  Ignore all matches ;
let str = "fdsfda323fdaf1232";
let reg = /\d+/;
let res = str.search(reg);
console.log(res);

Methods under regular objects

• test
• exec

// The regular way ;
// 1.test 2.exce;
let str = "dfasfd342234fda2342342f";
let reg = /\d+/;
let res = reg.test(str);
console.log(res); //true
let reg = /\d+/g;
let res = reg.exec(str);
console.log(res);
let res1 = reg.exec(str);
console.log(res1);

Metacharacters

. *(0 Times or more ) + ? $ ^ | \ () [] {
    };

• Non alphabetic characters with special meaning in regular expressions ;

​ Character category （Character Classes）

• .
  • Match line terminator （\n \r \u2028 or \u2029） Any single character other than
  • stay Character set （Character Sets） in ,. Will lose its special meaning , Represents the original value
• \
  • Escape character , It has two meanings
    • Indicates that the next character with a special meaning is literal
      • Indicates that the next character has a special meaning （ The result of escape is agreed in the metacharacter ）
• \d Match any Arabic numeral character
• \D Match any non Arabic character
• \w Match any （ Letter 、 Numbers 、 Underline ） The characters of
• \W Match any non （ Letter 、 Numbers 、 Underline ） The characters of
• \s Match a blank , Including Spaces 、 tabs 、 Page identifier 、 Line breaks and other Unicode Space
• \S Match a non blank character
• \t Match a horizontal tab （tab）
• \r Match a carriage return （carriage return）
• \n Match a line break （linefeed）
• \v Match a vertical tab （vertical tab）
• \f Match a page break （form-feed）

^ start   $  ending ; \w: Numbers   Letter   Underline ;

Character set

// []： Character set ;
// let str = "dffdabfds123fdabfdb435afdsa";
// let reg = /a|b/g;
// let reg = /[^ab]/g;
// let res = str.replace(reg,"*");
// console.log(res);
// let reg = /\d+/g;
// let reg = /[0-9]+/g;
// let res = str.replace(reg,"*");
// console.log(res);
// let reg = /[0-20]+/g;
// let res = str.replace(reg,"*");
// console.log(res);
// let str = "this knife is 5cM";
// let reg = /[kKCc]?[Mm]/;
// let res = str.replace(reg," rice ");
// console.log(res);

// . ===> [^\r\n]; \d===>[0-9];
// \w ===>[a-zA-Z_0-9];

[xyz]

• A character set , Also called character group . Match any character in the set . You can use hyphens ’-' Specify a range
• [xyz] Is an antisense or supplementary character set , Also called antisense character group . in other words , It matches any character that is not in parentheses . You can also use hyphens ‘-’ Specify a range of characters

/  Border character ：\b  :  Not  \w  Are called boundaries ;
// let str = "is this a book?";
// let reg = /\bis\b/g;
// let reg = new RegExp("\\bis\\b","g");
// let arr = str.match(reg);
// console.log(arr);

The border

• ^
  • Match input start . If more lines （multiline） The sign is set to true, The character will also match a line break （line break） The beginning after the symbol
• $
  • Match input end . If more lines （multiline） The sign is set to true, The character will also match a line break （line break） At the end of the front of the character
• \b
  • Match a zero width word boundary （zero-width word boundary）
• \B
  • Match a non-zero width word boundary （zero-width word boundary）

### grouping

• ( children )

  • have access to () Grouping expressions , Similar to grouping in Mathematics , Also known as children
  • Index grouping
  • Name groups
    • (?…)
    • groups attribute
  • Capture match
    • With capture （capturing） characteristic , The matching results will be saved to （ Subitem result ） in
    • (x)
  • Non capture match
    • No capture （capturing） characteristic , That is, the matching results will not be saved to （ Subitem result ） in
    • (?:x)
  • Zero width assertion / Pre check （Assertions）
    • Used to specify search in certain content ( But it doesn't include that ) Before or after
    • Forward zero width assertion / Pre check
      • sure
        • (?=pattern)
      • no
        • (?!pattern)
    • Negative zero width assertion / Pre check （ Be careful ：ES2018 newly added ）
      • sure
        • (?<=pattern)
      • no
        • (?<!patten)
  • The difference between capture and zero width assertion
    • Capture ： The matching content appears in the result but not in the subitem result
    • Zero width assertion ： It will not appear in the result

  backreferences

  • \n
    • there n Represents a variable , The value is a number , Point to... In the regular expression n A bracket （ Count from the left ） Substring matching in

// (): grouping ;
// let str = "abfdssafdsababljljabssfd";
// ?---{0,1} + --- {1,} * ---{0,} {2};
// let reg = /s{2}/g;
// let reg = /(ab){2}/g; //abb
// let res = str.replace(reg,"*");
// console.log(res);


// let str = "My name is Lilei";
// // LiLei Replace with Li Lei ;
// let reg = /Li(L|l)ei/g;
// let res = str.replace(reg," Li lei ");
// console.log(res);


//  Convert time format ：2019-10-19 ----> 19/10/2019;
//  backreferences ;
// let mytime = "2019-10-19";
// let reg = /(\d{4})-(\d{1,2})-(\d{1,2})/g;
// let res = mytime.replace(reg,"$3/$2/$1");
// // console.log( RegExp.$1 );
// console.log(res);


//  Name groups ;?< Group name > ES2018 New features ;
// let str = "$name=zhangsan&age=20";
// let reg = /\$(?<str>\w+)/;
// let res = str.match(reg);
// console.log(res.groups.str);


//  Zero width assertion ： positive （ Back ）  Negative （ front ） ---》  It must be asserted that 、 A negative assertion  ;
// es2018
//  Positive affirmation ;
// let str = "iphone3iphone4iphone11iphoneNumber";
// // iphone  Switch to “ Apple ”;
// let reg = /iphone(?=\d{1,2})/g;
// let res = str.replace(reg," Apple ");
// console.log(res);
//  Positive negative assertion ;
// let str = "iphone3iphone4iphone11iphoneNumber";
// // iphone  Switch to “ Apple ”;
// let reg = /iphone(?!\d{1,2})/g;
// let res = str.replace(reg," Apple ");
// console.log(res);


//  Negative positive assertion ;
// let str = "10px20px30pxipx";
// // px--> Pixels ;
// let reg = /(?<=\d{2})px/g;
// let res = str.replace(reg," Pixels ");
// console.log(res);
//  Negative negative assertion ;
// let str = "10px20px30pxipx";
// // px--> Pixels ;
// let reg = /(?<!\d{2})px/g;
// let res = str.replace(reg," Pixels ");
// console.log(res);

Quantitative vocabulary

• x{n}
  • n Is a positive integer . The previous pattern x Come on in succession n Time matching
• x{n,m}
  • n and m As a positive integer . The previous pattern x Continuous occurrence of at least n Time , at most m Time matching
• x{n,}
  • n Is a positive integer . The previous pattern x Continuous occurrence of at least n Time matching
• x*
  • Match the previous pattern x 0 Or many times
• x+
  • Match the previous pattern x 1 Or many times . Equivalent to {1,}
• x?
  • Match the previous pattern x 0 or 1 Time
• x|y
  • matching x or y

Matching mode

• g

  • global, Global mode ： Find all matches , Instead of stopping after the first match

• i

  • ignore, Ignore case mode ： Match is not case sensitive

• m

  • multiple, Multi line mode ： Will start and end characters （^ and $） Think of it as working on multiple lines , Instead of just matching the beginning and end of the entire input string

• s

  • dotAll / singleline Pattern ：. Can match newline

• u

  • unicode,unicode Pattern ： matching unicode Character set

     console.log(/^.$/.test("\uD842\uDFB7"));
     console.log(/^.$/u.test("\uD842\uDFB7"));
    

• y

  • sticky, Viscous mode ： Match regular lastIndex Property specifies the character of the position , And if there is no match, do not try to match from any subsequent indexes

• Regular tools http://regexper.com

//  Matching mode 
// g: The global matching 
// i: Ignore case ;
// let str = "afdafdAdfafd";
// let reg = /a/gi;
// let res = str.replace(reg,"*");
// console.log(res);


// m Multi line mode 
// let str = `adfsf
// dfdsa`;
// let reg = /^\w/gm;
// let res = str.replace(reg,"*");
// console.log(res);


// s .  Can match newline 
// let str = `<div>som
// e value..</div>`;
// let reg = /<div>.*<\/div>/gs;
// // “\”  escape ： Convert special meaning into literal meaning ;
// let res = reg.test(str);
// console.log(res);


// console.log(/^.$/.test("\uD842\uDFB7"));
// console.log(/^.$/u.test("\uD842\uDFB7"));

summary

​ 1） Regular creation

​ 2） Regular matching method

​ 3） Metacharacters

​ 4） Character set

​ 5） The border

​ 6） grouping

7） backreferences 

​ 8） Quantitative vocabulary

​ 9） Matching mode

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