Extendscript iterator

iterator.jsx

/**
* Constructs an iterator
* @example
* var it = new Iterator(layers);
* while (!it.atEnd)
* {
* 	it.next();
* 	var layer = layers[it.current];
*	//do something with the layer
*
* }
* @example
* var it = new Iterator(layers);
* function doSomething(layer) { //do something with one layer }
* it.do(doSomething);
* @class Iterator
* @classdesc An iterator object to use for easier loops
* @property {Array|Collection} list - An array or an After Effects Collection
* @param {Array|Collection} list - An array or an After Effects Collection
* @property {int} min - The minimum value (inclusive)
* @property {int} max - The maximum (inclusive)
* @property {int} length - The number of items
* @property {int} current - The current item number
* @property {boolean} atEnd - true if the iterator has reached the end
* @property {boolean} atStart - true if the iterator is at the start
* @property {boolean} valid - true if the iterator is between min and max. false until next() or previous() has been called at least once
* @property {boolean} isCollection - true if the list is a Collection, false if it's a controller
*/
function Iterator(list)
{
	this.min = 0;
	this.max = list.length -1;
	this.length = list.length;
	this.isCollection = false;
	if (list instanceof ItemCollection || list instanceof LayerCollection || list instanceof OMCollection || list instanceof RQItemCollection)
	{
		this.min = 1;
		this.max = this.length;
		this.isCollection = true;
	}
	this.current = -1;
	this.atStart = false;
	this.atEnd = false;
	this.valid = false;
	this.list = list;
}

/**
* Increments the Iterator<br />
* Must be called at least once to validate the iterator
*/
Iterator.prototype.next = function ()
{
	if (!this.valid)
	{
		this.goToStart();
	}
	else
	{
		if (this.current < this.max) this.goTo(this.current + 1);
	}

}

/**
* Decrements the Iterator
* if it's called while valid is false, goes to the end
*/
Iterator.prototype.previous = function ()
{
	if (!this.valid)
	{
		this.goToEnd();
	}
	else
	{
		if (this.current > this.min) this.goTo(this.current - 1);
	}
}

/**
* Goes to the end of the Iterator
*/
Iterator.prototype.goToEnd = function ()
{
	this.goTo(this.max);
}

/**
* Goes to the start of the Iterator
*/
Iterator.prototype.goToStart = function ()
{
	this.goTo(this.min);
}

/**
* Sets the iterator on the index
* @param {int} index - The index
*/
Iterator.prototype.goTo = function(index)
{
	this.current = index;
	if (this.current < this.min || this.current > this.max) this.valid = false;
	else this.valid = true;
	if (this.current == this.min) this.atStart = true;
	else this.atStart = false;
	if (this.current == this.max) this.atEnd = true;
	else this.atEnd = false;
}

/**
* Executes a function on each item of the List
* @param {function} callBack - The function to execute, which takes one parameter: an item of the list
*/
Iterator.prototype.do = function (callBack)
{
	var current = this.current;
	this.valid = false;
	this.atEnd = false;
	while(!this.atEnd)
	{
		this.next();
		callBack(this.list[this.current]);
	}
	this.goTo(current);
}