array.forEach

var a = ['a', 'b', 'c'];

a.forEach(function(element) {
    console.log(element
}

// a
// b
// c

arr.forEach(function callback(currentValue, index, array) {
    //your iterator
}[, thisArg]

var items = ['item1', 'item2', 'item3'];
var copy = [];

for (var i=0; i<items.length; i++) {
  copy.push(items[i])
}

var items = ['item1', 'item2', 'item3'];
var copy = [];

items.forEach(function(item){
  copy.push(item)
}

function logArrayElements(element, index, array) {
  console.log('a[' + index + '] = ' + element
}

// Notice that index 2 is skipped since there is no item at
// that position in the array.
[2, 5, , 9].forEach(logArrayElements
// logs:
// a[0] = 2
// a[1] = 5
// a[3] = 9

function Counter() {
  this.sum = 0;
  this.count = 0;
}
Counter.prototype.add = function(array) {
  array.forEach(function(entry) {
    this.sum += entry;
    ++this.count;
  }, this
  // ^---- Note
};

var obj = new Counter(
obj.add([2, 5, 9]
obj.count;
// 3 
obj.sum;
// 16

function copy(obj) {
  var copy = Object.create(Object.getPrototypeOf(obj)
  var propNames = Object.getOwnPropertyNames(obj

  propNames.forEach(function(name) {
    var desc = Object.getOwnPropertyDescriptor(obj, name
    Object.defineProperty(copy, name, desc
  }

  return copy;
}

var obj1 = { a: 1, b: 2 };
var obj2 = copy(obj1 // obj2 looks like obj1 now

var words = ['one', 'two', 'three', 'four'];
words.forEach(function(word) {
  console.log(word
  if (word === 'two') {
    words.shift(
  }
}
// one
// two
// four

// Production steps of ECMA-262, Edition 5, 15.4.4.18
// Reference: http://es5.github.io/#x15.4.4.18
if (!Array.prototype.forEach) {

  Array.prototype.forEach = function(callback/*, thisArg*/) {

    var T, k;

    if (this == null) {
      throw new TypeError('this is null or not defined'
    }

    // 1. Let O be the result of calling toObject() passing the
    // |this| value as the argument.
    var O = Object(this

    // 2. Let lenValue be the result of calling the Get() internal
    // method of O with the argument "length".
    // 3. Let len be toUint32(lenValue).
    var len = O.length >>> 0;

    // 4. If isCallable(callback) is false, throw a TypeError exception. 
    // See: http://es5.github.com/#x9.11
    if (typeof callback !== 'function') {
      throw new TypeError(callback + ' is not a function'
    }

    // 5. If thisArg was supplied, let T be thisArg; else let
    // T be undefined.
    if (arguments.length > 1) {
      T = arguments[1];
    }

    // 6. Let k be 0.
    k = 0;

    // 7. Repeat while k < len.
    while (k < len) {

      var kValue;

      // a. Let Pk be ToString(k).
      //    This is implicit for LHS operands of the in operator.
      // b. Let kPresent be the result of calling the HasProperty
      //    internal method of O with argument Pk.
      //    This step can be combined with c.
      // c. If kPresent is true, then
      if (k in O) {

        // i. Let kValue be the result of calling the Get internal
        // method of O with argument Pk.
        kValue = O[k];

        // ii. Call the Call internal method of callback with T as
        // the this value and argument list containing kValue, k, and O.
        callback.call(T, kValue, k, O
      }
      // d. Increase k by 1.
      k++;
    }
    // 8. return undefined.
  };
}