How to use Regular expression (Regexp) in Javascript?


This page is about regular expression in Javascript

Regular expressions operate at the level of code units. The single-character pattern (.) matches a single code unit (not a Text - Code point).



  • The pattern enclosed between slashes. Loaded compilation (only when the script is loaded)
var pattern = /ni.o/; 
  • Runtime compilation (when the script runs, the regexp pattern can be dynamic)
var pattern = new RegExp("ni.o", flags); 



var pattern = new RegExp("f.o","i"); 

Named Group

With named group

Named Group proposition

let re = /(?<year>\d{4})-(?<month>\d{2})-(?<day>\d{2})/u;
let result = re.exec('2015-01-02');
console.log(result.groups.year); // '2015'
console.log(result.groups.month); // '01'
console.log(; // '02';

console.log(result[0]); // '2015-01-02';
console.log(result[1]); // '2015';
console.log(result[2]); // '01';
console.log(result[3]); // '02';

Named Group Replacement

let re = /(?<year>\d{4})-(?<month>\d{2})-(?<day>\d{2})/u;
let result = '2015-01-02'.replace(re, '$<day>/$<month>/$<year>');
console.log(result);// '02/01/2015'
  • Routing
re = new RegExp("/api/profiles/(?<id>[^/]*)");
let result = '/api/profiles/1'.replace(re, 'backend/api/profiles/profile.js?id=$<id>');


const REGEXP_EXP = /^PREFIZ_/i;
const raw = Object.keys(process.env)
    .filter(key => REGEXP_EXP.test(key))
      (env, key) => {
        env[key] = process.env[key];
        return env;


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