array-iteration.js

var bind = require('../internals/function-bind-context');
var IndexedObject = require('../internals/indexed-object');
var toObject = require('../internals/to-object');
var toLength = require('../internals/to-length');
var arraySpeciesCreate = require('../internals/array-species-create');

var push = [].push;

// `Array.prototype.{ forEach, map, filter, some, every, find, findIndex, filterOut }` methods implementation
var createMethod = function (TYPE) {
  var IS_MAP = TYPE == 1;
  var IS_FILTER = TYPE == 2;
  var IS_SOME = TYPE == 3;
  var IS_EVERY = TYPE == 4;
  var IS_FIND_INDEX = TYPE == 6;
  var IS_FILTER_OUT = TYPE == 7;
  var NO_HOLES = TYPE == 5 || IS_FIND_INDEX;
  return function ($this, callbackfn, that, specificCreate) {
    var O = toObject($this);
    var self = IndexedObject(O);
    var boundFunction = bind(callbackfn, that, 3);
    var length = toLength(self.length);
    var index = 0;
    var create = specificCreate || arraySpeciesCreate;
    var target = IS_MAP ? create($this, length) : IS_FILTER || IS_FILTER_OUT ? create($this, 0) : undefined;
    var value, result;
    for (;length > index; index++) if (NO_HOLES || index in self) {
      value = self[index];
      result = boundFunction(value, index, O);
      if (TYPE) {
        if (IS_MAP) target[index] = result; // map
        else if (result) switch (TYPE) {
          case 3: return true;              // some
          case 5: return value;             // find
          case 6: return index;             // findIndex
          case 2: push.call(target, value); // filter
        } else switch (TYPE) {
          case 4: return false;             // every
          case 7: push.call(target, value); // filterOut
        }
      }
    }
    return IS_FIND_INDEX ? -1 : IS_SOME || IS_EVERY ? IS_EVERY : target;
  };
};

module.exports = {
  // `Array.prototype.forEach` method
  // https://tc39.es/ecma262/#sec-array.prototype.foreach
  forEach: createMethod(0),
  // `Array.prototype.map` method
  // https://tc39.es/ecma262/#sec-array.prototype.map
  map: createMethod(1),
  // `Array.prototype.filter` method
  // https://tc39.es/ecma262/#sec-array.prototype.filter
  filter: createMethod(2),
  // `Array.prototype.some` method
  // https://tc39.es/ecma262/#sec-array.prototype.some
  some: createMethod(3),
  // `Array.prototype.every` method
  // https://tc39.es/ecma262/#sec-array.prototype.every
  every: createMethod(4),
  // `Array.prototype.find` method
  // https://tc39.es/ecma262/#sec-array.prototype.find
  find: createMethod(5),
  // `Array.prototype.findIndex` method
  // https://tc39.es/ecma262/#sec-array.prototype.findIndex
  findIndex: createMethod(6),
  // `Array.prototype.filterOut` method
  // https://github.com/tc39/proposal-array-filtering
  filterOut: createMethod(7)
};