indexablemap.js

export const IndexableMap = class extends Map {
  constructor(iterable) {
    super();
    this._values = [];
    if (iterable != null) {
      for (const [key, value] of iterable) {
        this.set(key, value);
      }
    }
  }

  set(key, value) {
    this.delete(key);
    return super.set(key, this._values.push(value) - 1);
  }

  get(key) {
    const index = super.get(key);
    if (index != null) {
      return this._values[index];
    }
  }

  delete(key) {
    const index = super.get(key);
    if (index == null) {
      return false;
    }

    this._values.splice(index, 1);

    const keyIt = this.keys();
    for (;;) {
      const step = keyIt.next();
      if (step.done || step.value === key) {
        break;
      }
    }
    for (const k of keyIt) {
      super.set(k, super.get(k) - 1);
    }

    return super.delete(key);
  }

  clear() {
    this._values = [];
    return super.clear();
  }

  forEach(callback, thisArg) {
    for (const [key, value] of this) {
      callback.call(thisArg, value, key, this);
    }
  }

  *values() {
    yield* this._values;
  }

  at(index) {
    return this._values[index];
  }
};

function* entries() {
  const keyIt = this.keys();
  for (const value of this.values()) {
    yield [keyIt.next().value, value];
  }
}

const descriptor = {
  value: entries,
  writable: true,
  configurable: true,
};

Object.defineProperties(IndexableMap.prototype, {
  entries: descriptor,
  [Symbol.iterator]: descriptor,
});