Detect differences between two arrays.

Usage no npm install needed!

<script type="module">
  import arrayDiffItems from '';



A JavaScript module that finds the most ideal path to change an array to another array.



Most diff detecting library detects "Added", "Removed", "Unchanged" operations.

['Orange', 'Apple',  'Banana']
['Grape',  'Apples', 'Banana']


Removed: Orange
Removed: Apple
Added: Grape
Added: Apples
Unchanged: Banana

This kind of diff might be sufficient in many cases, but sometimes we want to detect "Change" rather than "Remove" then "Add".

['Orange', 'Apple',  'Banana']
['Grape',  'Apples', 'Banana']


Removed: Orange
Added: Grape
Changed: Apple => Apples
Removed: Banana
Added: Melon

array-diff-items solves this problem by introducing "cost" to change. It prefers "Change" when its cost to change a to b is less than simply removing a and adding b.


yarn add array-diff-items

Getting Started

import arrayDiffItems from 'array-diff-items';

// type Compare<T> = (left: T, right: T) => number;
// arrayDiffElements: <T>(left: T[], right: T[]) => (compare: Compare<T>) => DiffItem<T>[];
const left  = ['Banana', 'Apple', 'Orange',          'Grape'];
const right = [          'Apple', 'Orange', 'Melon', 'Grape Fruit'];

arrayDiffItems(left, right)((a, b) => {
  // Return the cost to change "a" to "b".
  // When cost is less than 1, that means changing "a" to "b" is preferable to removing "a" and then adding "a".
  if (a === b) return 0;
  if (a.startsWith(b) || b.startsWith(a)) return 0.5;
  return 2;
// [
//   {"type":"Removed","item":"Banana"},
//   {"type":"Unchanged","item":"Apple"},
//   {"type":"Unchanged","item":"Orange"},
//   {"type":"Added","item":"Melon"},
//   {"type":"Changed","left":"Grape","right":"Grape Fruit"}
// ]