Javascript - how to start forEach loop at some index

Question

I have an array with alot of items, and I am creating a list of them. I was thinking of paginating the list. I wonder how can I start a forEach or for

Answer 1

You could apply some kind of implementation of the iterator pattern.

var Iterator = function (list, position) {
  return {
    isNext: function () {
      return position + 1 < list.length;
    },
    isDefined: function () {
      return (position < list.length && position >= 0);
    },
    element: function () {
      return list[position];
    },
    position: function () {
      return position;
    },
    moveNext: function () {
      if (this.isNext()) { return Iterator(list, position + 1); }
      return Iterator([], 0);
    }      
}

Iterator.forEach = function (action, iterator, length) {
  var counter = 0;
  while (counter < length && iterator.isDefined()) {
    counter = counter + 1;
    action(iterator.element(), iterator.position());
    iterator = iterator.moveNext();
  }

  return iterator;
}   

And then have an iterator to use for going over the list and keep the state of the last iteration over a list.

var list = [1, 3, 5, 3, 6];
var iterator = Iterator(list, 0);

iterator = Iterator.forEach(function (element, index) {
  console.log(element, index);
}, iterator, 3);

//1 0
//3 1
//5 2

Iterator.forEach(function (element, index) {
   console.log(element, index);              
}, iterator, 5);

//3 3
//6 4