ArrayLazy.js

class ArrayLazy extends Array {
  _lazyQueue = [];
  map(callback) {
    this._lazyQueue.push({ type: "map", callback });
    return this;
  }
  filter(callback) {
    this._lazyQueue.push({ type: "filter", callback });
    return this;
  }
  collect() {
    const result = new ArrayLazy();
    collect: for (let i = 0; i < this.length; i++) {
      let value = this[i];
      for (let j = 0; j < this._lazyQueue.length; j++) {
        const { type, callback } = this._lazyQueue[j];
        if (type === "filter") {
          if (!callback(value)) continue collect;
        } else {
          // map
          value = callback(value);
        }
      }
      result.push(value);
    }
    this._lazyQueue = [];
    return result;
  }
}