List.js

list.js

// TODO: Add Validations
var List = function (value) {
  this.value = value || [];
};

List.prototype.unit = function (value) {
  return new List(value);
};

List.prototype.flatMap = function (fn, context) {
  var results = [];
  this.value.forEach(function (value, key, map) {
    var ret = fn.call(context, value, key, map);
    if (ret instanceof List) {
      ret = ret.get();
    }
    if (Array.isArray(ret)) {
      [].push.apply(results, ret);
    }
    else if (ret) {
      results.push(ret);
    }
  });
  return new List(results);
};

List.prototype.get = function () {
  return this.value;
};

List.prototype.map = function (fn) {
  return this.flatMap(function (x) {
    return this.unit(fn(x));
  }, this);
};

List.prototype.filter = function (fn) {
  return this.flatMap(function (x) {
    return fn(x) ? this.unit(x) : null;
  }, this);
};

List.prototype.filterNot = function (fn) {
  return this.flatMap(function (x) {
    return fn(x) ? null : this.unit(x);
  }, this);
};

var l = new List([1, 2, 3]);

var fn = function (val) {
  return [val, val*2, val*3];
};

var double = function (val) {
  return val * 2;
};

var even = function (val) {
  return val % 2 === 0;
};

console.log(l.flatMap(fn).get());
console.log(l.map(double).get());
console.log(l.filterNot(even).get());
console.log(l.filterNot(even).map(double).get());