What is regular

Re is a powerful tool for searching and replacing strings. Regular expressions (called ‘regexp’ or ‘reg’) contain patterns and modifiers

How to create re and basic usage

There are two syntax for creating regular expression objects, one is through the constructor, the new operator, which allows you to dynamically construct patterns from a string, when the regular expression will change, or when you don’t know what pattern in advance, you can use the constructor to create it, right

let reg = new RegExp('ice ice')// Create the re with the condition inside the first ""
console.log('My heart belongs to Wang Bingbing.'.search(reg))// 5 Returns the index of ice ice
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The other is the literal method, which is created with a slash ‘/’. The slash ‘/’ will tell JS that we are creating a re. When we know what mode to use and it will not change, we can create the re with the literal method

let reg=Ice ice / // Creates the re, '/ condition /' in the middle of the skew bar is the condition
console.log('My heart belongs to Wang Bingbing.'.search(reg)) //5 Returns the index of ice ice
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Special character character classes

The two simple little 🌰 above is an accurate match, we know who is, can create, but sometimes, we match is an uncertain character but know what type of time to do, for example, we come to find Bing Bing’s mobile phone number, ‘Wang Bing Bing’s mobile phone number is: 18888888888’, then I need to get ‘18888888888’, at this point the special character is used, we know the phone number is 0-9, then we can use \ D to get the number,

let reg=/\d/ // Create a re,
console.log('Wang Bingbing's mobile number is: 18888888888'.match(reg)) 
//["1", index: 9, input: "groups: undefined"]
// We see the first output ['1'] which is the result of our match
// index represents the index of the result
// Input represents what we are entering
// groups Indicates the group name
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‘18888888888’ is what we want. Don’t worry, we need to get one \d, we need to get multiple \d+

let reg=/\d+/ // Create a re,
console.log('Wang Bingbing's mobile number is: 18888888888'.match(reg)) 
// ["18888888888", index: 9, input: "groups: undefined] // [" 1888888888888 ", index: 9, input:" Groups: undefined]
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let reg=/^a? \d+$/ // Create a re that can start with a letter and end with a number
console.log('a18888888888'.match(reg)) 
// ["a18888888888", index:0, input: "a18888888888", groups: undefined]
console.log('18888888888'.match(reg)) 
// ["18888888888", index: 0, input: "18888888888", groups: undefined]
// Match a QQ mailbox
let email = '[email protected]'
let reg = /^\d+@\w+\.com$/;
console.log(email.match(reg));// ["[email protected]"]
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Special character symbol class

In the qq mailbox example above, if not com end but cn at the end of it, then how to match, then can use | said or

// Match a QQ mailbox
let email = "[email protected]";
let email2 = "[email protected]";
let email3 = "[email protected]";
let reg = /^\d+@\w+(\.\w+)+\1? /;
let reg1 = /^\d+@\w+\.(com|cn)$/;
console.log(email.match(reg1)); // ["[email protected]", ".com"]
console.log(email2.match(reg)); // ["[email protected]", ".cn"]
console.log(email3.match(reg)); // ["[email protected]", ".cn"]
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// Match a mobile phone number with 11 digits starting with super 13, 15, 17, and 18
let tel = "18787875678";
let tel1 = "12787875678";
let reg = / ^ 1,5,7,8 [3] \ d {9} $/;
console.log(tel.match(reg)); / / / "18787875678"
console.log(tel1.match(reg)); //null
// Matches the first four digits of a landline number - the link is followed by 7 or 8 digits
let tel = "0100-89087678";
let tel1 = "010-89087678";
let reg = / ^ \ d {3, 4} - \ d {7, 8} $/;
console.log(tel.match(reg)); / / / "0100-89087678"
console.log(tel1.match(reg)); / / / "010-89087678"
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methods

We’ve been using the match method up here, which returns an array and returns NULL if there’s no match. There are other ways

let tel = "0100-89087678";
let tel1 = "010-89087678";
let reg = / ^ \ d {3, 4} - \ d {7, 8} $/;
console.log(reg.exec(tel1)); / / / "0100-89087678"
console.log(reg.test(tel)); //true
console.log(tel.match(reg)); / / / "0100-89087678"
console.log(tel.search(reg)); / / 0
console.log(
tel.replace(reg, function () {
return "*".repeat(10); }));/ / * * * * * * * * * *
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Advanced search

Regular expressions have six optional arguments (flags) to allow global and case-insensitive searches, etc. These parameters can be used alone or together in any order and are included in the regular expression instance.

let str = "This this this";
let reg1 = /t/i; // Match t is case insensitive
let reg2 = /t/g; // Global match t
let reg3 = /t/gi;  // Global matching t is case insensitive
console.log(str.match(reg1)); // ['T']
console.log(str.match(reg2)); // ["t", "t"]
console.log(str.match(reg3)); // ["T", "t", "t"]
    
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Assertions to find

// Hide the phone number
let tel = "18787875678";
let reg = / (? <=\w{3})\w+(? =\w{4})/; 
tel.replace(reg, () = > {
  return "*".repeat(4);
});
/ / "187 * * * * 5678"
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