Entity Manager

The best implementation of how to store and manage game objects

When creating a game, have you ever wondered which way to store game objects is the best? array, object or maybe Map?
For this example I will use a particle system, but it could be anything.

Demo: https://murka007.github.io/Entity-Manager/

Comparing different ways

I will explain all scenarios why you shouldn't use only one way of storing objects.

Array

Open Array

This method of storing objects is quite simple, but it is too slow.
To remove an entity, you will need to iterate through the entire array.

const entities = [];
function add(entity) {
    entities.push(entity);
}

function remove(id) {
    for (let i=0;i<entities.length;i++) {
        if (entities[i].id === id) {
            entities.splice(i, 1);
            break;
        }
    }
}

Another option is to use array as an object, to use entity ids as keys.
But to iterate correctly we need to check for empty indexes in the array

function add(entity) {
    entities[entity.id] = entity;
}

function remove(entity) {
    entities[entity.id] = null;
}

// iterate over array, ignore empty indexes
for (let i=0;i<entities.length;i++) {
    if (!entities[i]) continue;
    
    // rendering, some math operations etc
}

Object

Open Object

I don't recommend using this method to anyone, iteration speed is extremely low.

const entities = {};
function add(entity) {
    entities[entity.id] = entity;
}

function remove(entity) {
    delete entities[entity.id];
}

Map

Open Map

Map is good to store objects, it's behaviour is the same as that of an object and array. Also it is a bit slower than array

const entities = new Map();
function add(entity) {
    entities.set(entity.id, entity);
}

function remove(entity) {
    entities.delete(entity.id);
}

We figured out that some ways are good, and some of them are bad, but now I will show you the best way to store objects.

Implementation

My implementation you can find here: EntityManager

Entity manager class has 4 properties:

• id we will use it to get the length of the array, it is faster than using arr.length
• entities used to store all of your entities, you can use it to iterate through it
  • there's no empty slots, so you don't have to check for it
• link Map object that stores links between entity ids and their index in the entities array
  • It is necessary, so we don't have to iterate through array
• unused list of unused ids, we should reuse previous ids in order not to increment id

Note: In your entity class, id property should equal to -1 before you will call add method