Modified getify/deePool with additional functionality

ObjectPool.js

// modified https://github.com/getify/deePool

const EMPTY_SLOT = Object.freeze(Object.create(null));

export default class ObjectPool {
  constructor(objectFactory = () => {}, initialSize) {
    this.objectFactory = objectFactory;
    this.objPool = [];
    this.nextFreeSlot = null;
    if (!!initialSize) this.grow(initialSize);
  }

  pop() {
    if (this.nextFreeSlot == null || this.nextFreeSlot == this.objPool.length) {
      this.grow(this.objPool.length || 5);
    }

    const objToUse = this.objPool[this.nextFreeSlot];
    this.objPool[this.nextFreeSlot++] = EMPTY_SLOT;
    return objToUse;
  }

  push(obj) {
    if (this.nextFreeSlot == null || this.nextFreeSlot == -1) {
      this.objPool[this.objPool.length] = obj;
    } else {
      this.objPool[--this.nextFreeSlot] = obj;
    }
  }

  grow(count = this.objPool.length) {
    if (count > 0 && this.nextFreeSlot == null) {
      this.nextFreeSlot = 0;
    }

    if (count > 0) {
      const curLen = this.objPool.length;
      this.objPool.length += Number(count);

      for (let i = curLen, il = this.objPool.length; i < il; i++) {
        this.objPool[i] = this.objectFactory();
      }
    }

    return this.objPool.length;
  }

  size() {
    return this.objPool.length;
  }

  numEmpty() {
    return this.objPool.filter((value) => value === EMPTY_SLOT).length;
  }

  numStored() {
    return this.objPool.length - this.numEmpty();
  }

  toString() {
    return "[ ObjectPool { available:" + this.numStored() + "/" + this.objPool.length + " } ]";
  }

  forEach(callback = () => void 0) {
    this.objPool.forEach((value, index, array) => {
      if (value !== EMPTY_SLOT) callback(value, index, array);
    });
  }
}