regular expression

 RegExp -  Regular expressions

    It can also be called  " Regular expressions "

         It's a complex data type

         effect :

          1.  It is specially used to verify whether the string conforms to the rules

          2.  Get part of the content that conforms to the rules from the string

         Usage method :

           Use some specific symbols ,  To form an expression

         Use this expression to validate the string ,  Or get some content from the string

Create a regular expression

        1.  Literal form creation

          

// 1.  Literal creation
 const reg = /abcd/;
 console.log(reg);
 console.log(typeof reg);

        2.  Built in constructor creation

// 2.  Built in constructor creation
 const reg2 = new RegExp('abcd');
 console.log(reg2);
 console.log(typeof reg2);

         significance :  The string contains a paragraph  abcd  Just letters

           testing : aaabbbcccddd  unqualified

           testing : aaabcddddd    qualified

Two methods of regular expression

       

 

1.  matching :

 

  Verify whether the string conforms to the regular rules

           Usage method :  Regular .test( The string you want to detect )

           Return value :  A Boolean value , true  perhaps  false

 

 

2.  Capture : 

  Get the fragment that conforms to the regular rules from the string

           Usage method :  Regular .exec( The string you want to capture )

           Return value :

            1.  There is no regular slice in the string

            2.  There are regular fragments in the string

             

 2-1.  Basic capture

                 The return value is an array

                [0]  It's a captured fragment

                 No matter how many clips there are ,  Just capture the first clip

                 No matter how many times you catch ,  It's the first clip

              

2-2.  When a regular expression has  ()  When

                 The return value is an array

                 from   Indexes [1]  Start with a separate capture of each parenthesis

             

 2-3.  When regular has a global identifier  g  When

                 The second capture will continue to look backward from the end of the first capture

                 Until you can't find the location ,  return  null

                 Capture again later ,  Still from  [0]  Location start search

 const reg = /abcd/;
// 1. test()
 console.log(reg.test('aaabbbcccddd'));
 console.log(reg.test('aaabcddddd'));
// 2. exec()
 const res = reg.exec('aaabbbcccddd')
 console.log(res);
 const res2 = reg.exec('aaabcdddddabcdabcd');
 console.log(res2);

  Metacharacters of regular expressions  -  Basic metacharacter

         Metacharacters :  The basic symbols that make up a regular

           Replace the text content with symbols

           Put all the text content into some symbols to replace

 

 1. \s （ A lowercase letter ）   Represents a space

 1. \s
 //  Indicates that there needs to be one in the string   Space   character
 const reg = /\s/ ;//  Equivalent to  / / 
 console.log(reg.test(' abcdefg'));
 console.log(reg.test('abc d efg'));

      2. \S（ Capitalization ）    Represents a non space

 

// \S
 //  Indicates that there needs to be one in the string   Non blank space   character
 const reg = /\S/
 console.log(reg.test(' a'))
 console.log(reg.test(' a a a '))

      3. \t    Represents a tab (tab)

// 3. \t
//  Indicates that there needs to be a... In your string   tabs   character
 const reg = /\t/
 console.log(reg.test(' ')) //  Two spaces
 console.log(reg.test(' ')) //  A tab

       A tab is a tab ,  Not multiple spaces .

      4. \d    Represents a number

// \d
 //  Indicates that there needs to be a... In your string   Numbers   character
 const reg = /\d/
 console.log(reg.test('abcdef'))
 console.log(reg.test('ab1c1d111ef'))

      5. \D    Represents a non number

// \D
 //  Indicates that there needs to be a... In your string   The digital   character
 const reg = /\D/
 console.log(reg.test('1234567890'))
 console.log(reg.test('12a34a5a67a890'))

      6. \w    It means a   Alphanumeric underline

 

 // \w
 //  Indicates that there needs to be a... In your string   Numbers or letters or underscores   character
 const reg = /\w/
 console.log(reg.test('[email protected]#$%$#@#$%$#$%$#$%$#'))
 console.log(reg.test('[email protected]#123123$%$#@#$%$#$%asdasd$#$%$#'))

         Express   Numbers   Letter   Underline   Choose one of three   There has to be one

      7. \W    It means a   Non alphanumeric underline

// \W
 //  Indicates that there needs to be a... In your string   Alphanumeric underline   Characters other than
 const reg = /\W/
 console.log(reg.test('asdasd123123123____'))
 console.log(reg.test('asdasd123123123____%'))
 console.log(reg.test('asdasd12312312##3____'))

         Express   Numbers   Letter   Underline   Any other one will do

      8.  spot (.)  Represents any character that is not newline

//  spot (.)
 //  Indicates that there needs to be a... In your string   Non newline   Content
 const reg = /./
 console.log(reg.test('\n'))
 console.log(reg.test('a\nb'))
 console.log(reg.test(' \n'))

      9.  Oblique line (\)  The escape sign

         Transform meaningless content into meaningful content

         Transform meaningful content into meaningless content

 //  Oblique line (\)
 //  Indicates that there needs to be a letter in your string  s
 const reg = /s/
 console.log(reg.test('abcd'))
 console.log(reg.test('abcds'))

 //  Indicates that there needs to be a... In your string   Space character
 const reg2 = /\s/
 console.log(reg2.test('abcdssss'))
 console.log(reg2.test('abcdssss '))

 //  Indicates that there needs to be a... In your string   Non newline   Any character of
 const reg3 = /./
 console.log(reg3.test('asday'))

 //  Indicates that there needs to be a... In your string   spot   Text
 const reg4 = /\./
 console.log(reg4.test('asdasd'))
 console.log(reg4.test('asdasd.'))

 //  Indicates that there needs to be a... In your string  \  Text
 const reg5 = /\\/
 console.log(reg5.test('\\'))