Regular match same character

In many interview questions, I have seen some operations on the same character in a string , Most people will use the traversal method to get the same characters , But regularization can also meet some of our requirements .

grammar

()\n

Matching the same characters requires \ This metacharacter , And this metacharacter must match () Use .

give an example
Find the same two numbers

'1122'.match(/(\d)\1/g)  //["11", "22"]

Deduce
Sometimes we need more than two identical numbers , We can continue in the future \1 operation

Find the same three characters

'112aadddddw2'.match(/(.)\1\1/g)  //["ddd"]

You may not understand the number of the same characters , Actually, we can take it apart ,() Match once ,\1 Match once , Two \1 Just twice , Three times in all . Of course , It must be quite troublesome to match multiple times , So you can use {} Conduct \1 Replacement .

'112aadddddw2'.match(/(.)\1{2}/g)  //["ddd"]

stay \1 Use... In the back {} That is to say \1 The number of .

Be careful ：
Some people will certainly ask since \1 Indicates the previous () What's in it , that \2 Well , perhaps \n Well
Actually ,\1 Reference is made to the 1 Sub expression ,\2 Reference is made to the 2 Sub expression .

// Find a two digit number followed by a three letter character 
/(\d)\1(\w)\2{2}/.test('x222aaas')  // true
// Find a number repeated twice followed by a letter and finally followed by a letter 
/(\d(\w))\1\2/.test('2w2ww')   // true