Polyfill for the Map in Js

map-polyfill.js

class BetterMap {
  constructor(init) {
    this.clear()
    if (init)
      for (var i = 0; i < init.length; i++)
        this.set(init[i][0], init[i][1])
  }
  clear() {
    this._map = {}
    this._keys = []
    this.size = 0
  }
  get(key) {
    return this._map["map_" + key]
  }
  set(key, value) {
    this._map["map_" + key] = value
    if (this._keys.indexOf(key) < 0)
      this._keys.push(key)
    this.size = this._keys.length
    return this
  }
  has(key) {
    return this._keys.indexOf(key) >= 0
  }
  delete(key) {
    var idx = this._keys.indexOf(key)
    if (idx < 0)
      return false
    delete this._map["map_" + key]
    this._keys.splice(idx, 1)
    this.size = this._keys.length
    return true
  }
  keys() {
    return {
      _keys: this._keys,
      _idx: 0,
      next: function () {
        if (this._idx < this._keys.length)
          return {
            value: this._keys[this._idx++],
            done: false
          }
        return {
          value: undefined,
          done: true
        }
      }
    }
  }
  forEach(callback, thisArg) {
    for (var i = 0; i < this._keys.length; i++)
      callback.call(thisArg, this._map["map_" + this._keys[i]], this._keys[i], this)
  }
}