Compare two texts and find differences using LCS (Longest Common Subsequence) algorithm. Side-by-side diff visualization. Zero-dependency text comparison tool.

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This package is part of DevKits — 82+ free developer tools. The online Diff Checker offers side-by-side visualization and merge conflict resolution.

→ Try Side-by-Side Diff View

Installation

npm install @devkits/diff-checker

Usage

const { compare, getStats, unified, summarize } = require('@devkits/diff-checker');

const original = `Hello World
This is a test
Goodbye`;

const modified = `Hello JavaScript
This is a test
Farewell`;

// Get detailed line-by-line diff
const diff = compare(original, modified);
// [
//   { type: 'remove', left: 'Hello World', lNum: 1 },
//   { type: 'add', right: 'Hello JavaScript', rNum: 1 },
//   { type: 'equal', left: 'This is a test', right: 'This is a test', lNum: 2, rNum: 2 },
//   { type: 'remove', left: 'Goodbye', lNum: 3 },
//   { type: 'add', right: 'Farewell', rNum: 3 }
// ]

// Get statistics
const stats = getStats(diff);
// { added: 2, removed: 2, unchanged: 1 }

// Generate unified diff format
const uDiff = unified(original, modified);
// --- original
// +++ modified
// -Hello World
// +Hello JavaScript
//  This is a test
// -Goodbye
// +Farewell

// Get simple summary
const summary = summarize(original, modified);
// {
//   added: ['Hello JavaScript', 'Farewell'],
//   removed: ['Hello World', 'Goodbye'],
//   summary: '2 addition(s), 2 deletion(s)'
// }

// Ignore whitespace differences
const diffNoWs = compare('Hello  World', 'Hello World', { ignoreWhitespace: true });
// Shows as equal

// Ignore case differences
const diffNoCase = compare('Hello', 'hello', { ignoreCase: true });
// Shows as equal

API

`compare(left, right, options)`

Compares two texts line by line using LCS algorithm.

Options:

ignoreWhitespace: Ignore whitespace differences (default: false)
ignoreCase: Ignore case differences (default: false)

Returns array of diff items with type: 'equal', 'add', or 'remove'.

`getStats(diff)`

Returns statistics: {added, removed, unchanged} counts.

`unified(left, right, options)`

Generates unified diff format (like diff -u).

`summarize(left, right, options)`

Returns simple summary with added/removed lines and count summary.

Algorithm

Uses the Longest Common Subsequence (LCS) algorithm to find the minimum set of changes needed to transform the original text into the modified text.

Time complexity: O(m × n) where m and n are the number of lines in each text.

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License

MIT

Keywords

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Package last updated on 11 Mar 2026

devkits-diff-checker