A Map-like data structure for Identifiable values that provides many array-like operations as well

Usage no npm install needed!

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



A thin wrapper around Array and some Maps that provides relatively efficient array-like and map-like methods and functions. Index-based operations and key-based operations are both usually constant time.


My JavaScript and TypeScript work is all frontend work, specifically single page apps with React. When working on such applications, almost all the data I work with has an "id" field of some kind. This is usually a string, number, or uuid, which I just model as a string in TS.

I find myself needing to update or remove elements by ID, but also needing array-like operations such as map and filter (plus some other operations that I miss from other languages!). Sometimes I use a Map, but then I can't access elements by index or push something to the end, so most often I'm just using Array, which of course does not know that my elements all have unique IDs.

Enter ArrayMap, which does both. In addition to the usual suspects of put, get, push, map, and filter, it provides some additional operations such as collect, groupBy, sortByKey, and more.

I find this to be a highly convenient solution that makes state management much easier when building my applications.


ArrayMap does its best to be efficient, but it is primarily about convenience and correctness, not performance. Since ArrayMap has to maintain additional information about the position of each key within the primary array, some of the operations are a bit more expensive, notably 'remove'. However, it should be more than fast enough for any reasonable frontend use case. Don't build a game-engine on top of it.

The Basics

ArrayMap works with any type T, but it needs to know how to get the ID of that type. It does this with the provided identify function which takes a T and returns its ID. For example, if we had a user named Alex and a User model type:

interface User {
  id: number;
  name: string;
  email: string;
const alex = { id: 1, name: "Alex", email: "" };

We could add Alex to our users collection like so:

import ArrayMap from "arraymap-js"; 
const users = ArrayMap.empty(user =>;
const users = ArrayMap.fromArray([alex], user =>;


IDE dot completion is your friend here, as the names, docstrings, and types of every method should explain its usage. For constructors, try ArrayMap.. For operations on an ArrayMap x, try x.