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Regular Expressions

RegEx is a powerful tool used for matching patterns within strings.

Creating RegExp object​

There are two primary ways to create a RegExp object in JavaScript

Literal notation​

const regex = /abc/i; // 'abc' pattern, case-insensitive

Constructor function​

const regex = new RegExp('abc', 'i'); // 'abc' pattern, case-insensitive

Methods​

test()​

Tests for a match in a string and returns true or false.

const regex = /abc/;
console.log(regex.test('abcdef')); // true

exec()​

Executes a search for a match in a string and returns an array of results or null.

const regex = /abc/;
console.log(regex.exec('abcdef')); // ["abc"]

Basic syntax1​

Characrer Classes​

[ ] Match any one of the specified characters.

const regex = /[abc]/; // Matches 'a', 'b', or 'c'
const regex = /[a-z]/; // Matches all charachters from 'a' to 'z'

Metacharacters​

Special characters with specific meanings.

  • . Any character except newline.
  • \d Any digit.
  • \w Any word character (alphanumeric + underscore).
  • \s Any whitespace character.
  • ^ Start of the string.
  • $ End of the string.
const regex = /\d+/; // Matches one or more digits

Quantifiers: Specify the number of occurrences​

    • * 0 or more times.
    • + 1 or more times.
  • ? 0 or 1 time.
  • {n} Exactly n times.
  • {n,} n or more times.
  • {n,m} Between n and m times.
const regex = /a{2,4}/; // Matches 'aa', 'aaa', or 'aaaa'

Grouping and Alternation​

  • ( ) Grouping.
  • | Alternation (OR).
const regex = /(abc|def)/; // Matches 'abc' or 'def'

Footnotes​

  1. https://regex101.com ↩