map-push

Pushes new items to Array entries of a Map

Introduction

Sometimes you have a Map with entries of type Array and you want to push new items to those entries.
You also want to create a new Array initialized with the item you want to push if an entry for a particular key does not exist yet.

To do that, I always end up doing something along the lines of:

const myMap = new Map();
const anItem = toPush;
const aKey = "some-key";

if (myMap.Has(aKey)) {

  const arrayEntry = myMap.get(aKey);
	
  arrayEntry.push(anItem);

}
else {

  myMap.set(aKey, [anItem]);

}

Which is boring, long and does not handle edge cases.
So I thought: maybe I can write an utility function for that. Enter map-push.

map-push exposes is a function called mapPush that encapsulates the code above and handles a few edge cases.
What edge cases does mapPush handles, you say ? Well...

• mapPush will check if the entry is in fact an Array before pushing, and if not will fallback to use Map.set().
• mapPush will check if the Map to change is actually a Map and is not null or undefined.
• mapPush will create a new Array only if the Map does not have entries for the key given.

So, how do you use mapPush ?

Usage

mapPush has the following signature: mapPush(map, key, value)
You have to pass a Map, the key of an entry (that might not exists) and a value.
In return you will get new length of the Array (like Array.push()).

The NPM package is hybrid, that means that you get both the ES Modules and the CommonJS version.

With CommonJS

const { mapPush } = require('map-push/cjs');

Note: Import from /cjs folder !

With ES Modules

import { mapPush } from 'map-push'

What about installation ? You have two options...

Installation

You can get mapPush on NPM by running npm install map-push.
Or, as this is a small utility function, I suggest to simply copy/paste it and skipping NPM.