JS filter, map and reduce - homemade

arrayFunctions.js

// MAPPY
Array.prototype.mappy = function(fn, that) {
  var out = [],
      x,
      that = that || {};

  for (var i = 0; i < this.length; i++) {
    x = fn.call(that, this[i], i, this);
    out.push(x);
  }
  return out;
};

// FILTERY
Array.prototype.filtery = function(fn, that) {
  var out = [],
      flag,
      that = that || {};

  for (var i = 0; i < this.length; i++) {
    flag = fn.call(that, this[i], i, this);
    if (flag) {
      out.push(this[i]);
    }
  }
  return out;
}

// REDUCY
Array.prototype.reducy = function(fn, initial){
  var res,
      accumulator,
      i = (initial)? 0: 1;
    
  for (i; i < this.length; i++) {
    accumulator = fn.call(
      this,
      accumulator || initial || this[i-1],
      this[i],
      i,
      this
    );
  }
  return accumulator;
}

var data = [
  {id: 1, name: 'mike', power: 12},
  {id: 2, name: 'julia', power: 10},
  {id: 3, name: 'troy', power: 5},
  {id: 4, name: 'sarah', power: 2},
  {id: 5, name: 'truls', power: 8}
];

var res = data
  .filtery(function(o){
    return o.id > 2;
  })
  .mappy(function(o){
    return o.power;
  })
  .reducy(function(base, item){
    return base + item;
  });

console.log(res);

// DEMO at http://codepen.io/KarlPokus/pen/oXQrWg?editors=0012

Update reducy to include correct default for initial value as 2nd arg and all the args to the callback. Kinda terse but simple enough to read me thinks.