Basic Implementation of the array filter

myArrayFilter.js

Array.prototype.xfilter = myCustomArrayFilter;

function myCustomArrayFilter (action) {
  var result = [];
  for (var i = 0; i < this.length; i++) {
    var args = [this[i], i, this];
    if (action.apply(null, args)) {
      result.push(this[i]);
    }
  }
  return result;
}

var greaterThen4 = [4, 5, 6].xfilter(x => x > 4);
console.log(greaterThen4, 'filter')