better-regex

A regex engine built from scratch in vanilla JavaScript — a hand-written parser and a backtracking matcher. No native RegExp, no dependencies. Built as a learning project to understand how regex engines actually work under the hood.

Install

npm i @rabia_youcef/better-regex

Usage

const { match } = require("@rabia_youcef/better-regex")

match("cat|dog", "cat")     // true
match("a+b", "aaab")        // true
match("colou?r", "color")   // true
match("(ab)+", "abab")      // true
match("(cat|dog)s", "dogs") // true
match("a(b|c)d", "abd")     // true

match(pattern, input) returns true if the pattern matches the entire input string, else false.

Supported

| Syntax | Meaning | |---|---| | abc | literal characters | | . | any single character | | * | zero or more | | + | one or more | | ? | zero or one | | \| | alternation (or) | | ( ) | grouping (with full nesting) |

How it works

Two phases. A parser turns the pattern into a tree using recursive descent — alternation, sequences, and groups each handled by their own function, with groups recursing back into the parser so patterns can nest arbitrarily. Then a backtracking matcher walks the tree against the input, threading the position through each node and backing off when a greedy quantifier overshoots — the same backtracking that powers real-world regex engines.

Roadmap

• Character classes [a-z]
• Anchors ^ $
• Escape sequences \d \w \s

License

MIT