altArray.js

class AltArray extends Array {
  constructor(...args) {
    super(...args);
  }

  altMap(fn) {
    var newArr = []
    for (let i = 0; i < this.length; i++) {
      newArr.push(fn(this[i], i, this));
    }
    return newArr;
  }

  altForEach(fn) {
    for (let i = 0; i < this.length; i++) {
      fn(this[i], i, this);
    }
  }

  altReduce(fn, initialValue) {
    var i = arguments.length > 1 ? 0 : 1;
    var acc = arguments.length > 1 ? initialValue : this[1];

    for (i; i < this.length; i++) {
      acc = fn(acc, this[i], i, this)
    }
    return acc;
  }
}