Regular Expressions Explained

Key Concepts

Pattern Matching
Character Classes
Quantifiers
Anchors
Groups and Backreferences

Pattern Matching

Pattern matching is the core concept of regular expressions, where a specific pattern is defined to search for within a string. This pattern can be a simple sequence of characters or a complex combination of characters and special symbols.

Example:

let pattern = /hello/;
let text = "hello world";
console.log(pattern.test(text)); // Outputs: true

Character Classes

Character classes allow you to define a set of characters that can match at a given point in the pattern. Common character classes include [abc] (matches any one of 'a', 'b', or 'c'), \d (matches any digit), and \w (matches any word character).

Example:

let pattern = /[aeiou]/;
let text = "hello";
console.log(pattern.test(text)); // Outputs: true

Quantifiers

Quantifiers specify how many instances of a character, group, or character class must be present in the input for a match to be found. Common quantifiers include * (zero or more), + (one or more), and ? (zero or one).

Example:

let pattern = /go*d/;
let text = "good";
console.log(pattern.test(text)); // Outputs: true

Anchors

Anchors are used to specify the position of the pattern within the string. Common anchors include ^ (start of the string) and $ (end of the string).

Example:

let pattern = /^hello$/;
let text = "hello";
console.log(pattern.test(text)); // Outputs: true

Groups and Backreferences

Groups allow you to treat multiple characters as a single unit. Backreferences allow you to refer to a previously matched group within the same regular expression. Groups are created using parentheses (), and backreferences are denoted by \1, \2, etc.

Example:

let pattern = /(\w+)\s\1/;
let text = "hello hello";
console.log(pattern.test(text)); // Outputs: true