Fun with js functions. Just decided in implement my own version of map, filter, foldl, along with a few helper functions.

fun_with_functions.js

Array.prototype.forEach = function (fun) {
  for (var i = 0; i < this.length; i++) {
    fun(this[i]);
  }
};

Array.prototype.foldl = function (acc, fun) {
  this.forEach(function (elem) {
    acc = fun(elem, acc);
  });
  return acc;
}
Array.prototype.filter = function (fun) {
  var result = [];
  this.forEach(function (elem) {
    if (fun(elem)) { 
      result.push(elem); 
    }
  });
  return result;
}
Array.prototype.map = function (fun) {
  var result = [];
  this.forEach(function (elem, i) {
    result.push(fun(elem));
  });
  return result;
}

// additional bool logic functions

function not (f) {
  return function (e) { return !f(e); }; 
}
function even (num) { return (num % 2) == 0; }
function odd (num) { return not(even)(num); }

function greaterThan(num1, num2) {
  return num1 > num2;
}
function lesserThan(num1, num2) {
  return num1 < num2;
}

function and (case1, case2) {
  return function (e) {
    return case1(e) && case2(e);
  };
}
function or (case1, case2) {
  return function (e) {
    return case1(e) || case2(e);
  };
}

// additional manlipulation functions

function square(num) {
  return num * num;
}
function times(mulitplicant) {
  return function (num) {
    return num * mulitplicant;
  };
}
function mod (amount) {
  return function (num) {
    return num % amount;
  };
}

// generate list

function range(from, to, stepRange) {
  
  var direction = from < to ? 1 : -1;
  var result    = [];
  var step      = ( stepRange !== undefined ? stepRange : 1) * direction;
  var condition	= direction < 0 ? greaterThan : lesserThan;
  
  if (step !== 0) {
    for (var i = from; condition(i, to + direction); i += step) {
      result.push(i);
    }
  }
  return result;
}