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LazyLoad

LazyLoad is a plugin that allows you to defer image loading until the image is scrolled to.

Plugin Code (Version 1.0)

var LazyLoad = new Class({

	Implements: [Options,Events],

	/* additional options */
	options: {
		range: 200,
		image: 'blank.gif',
		resetDimensions: true,
		elements: 'img',
		container: window,
		fireScroll: true,
		mode: 'vertical'
	},

	/* initialize */
	initialize: function(options) {
	
		/* vars */
		this.setOptions(options);
		this.container = document.id(this.options.container);
		this.elements = $$(this.options.elements);
		var axis = (this.options.mode == 'vertical' ? 'y': 'x');
		this.containerDimension = this.container.getSize()[axis];
		this.start = 0;

		/* find elements remember and hold on to */
		this.elements = this.elements.filter(function(el) {
			/* reset image src IF the image is below the fold and range */
			if(el.getPosition(this.container)[axis] > this.containerDimension + this.options.range) {
				el.store('oSRC',el.get('src')).set('src',this.options.image);
				if(this.options.resetDimensions) {
					el.store('oWidth',el.get('width')).store('oHeight',el.get('height')).set({'width':'','height':''});
				}
				return true;
			}
		},this);
	
		/* create the action function */
		var action = function() {
			var cpos = this.container.getScroll()[axis];
			if(cpos > this.start) {
				this.elements = this.elements.filter(function(el) {
					if((this.container.getScroll()[axis] + this.options.range + this.containerDimension) >= el.getPosition(this.container)[axis]) {
						if(el.retrieve('oSRC')) { el.set('src',el.retrieve('oSRC')); }
						if(this.options.resetDimensions) {
							el.set({
								width: el.retrieve('oWidth'),
								height: el.retrieve('oHeight') 
							});
						}
						this.fireEvent('load',[el]);
						return false;
					}
					return true;
				},this);
				this.start = cpos;
			}
			this.fireEvent('scroll');
			/* remove this event IF no elements */
			if(!this.elements.length) {
				this.container.removeEvent('scroll',action);
				this.fireEvent('complete');
			}
		}.bind(this);
	
		/* listen for scroll */
		this.container.addEvent('scroll',action);
		if(this.options.fireScroll) { this.container.fireEvent('scroll'); }
	}
});

/* usage */
window.addEvent('domready',function() {
	var lazyloader = new LazyLoad();
});

Options and Events

Options for LazyLoad include:

• range: (defaults to 200) The amount of space from the container’s bottom position that you want to look for images to load.
• image: (defaults to “blank.gif”) The image to replace the original image.
• resetDimensions: (defaults to true) Removes the image’s width and height attributes.
• elements: (defaults to “img”) Images to consider for lazy loading.
• container: (defaults to window) The container for which to look for images within.
• mode: (defaults to “vertical”) The mode for which the plugin will adjust to.

Events for LazyLoad include:

• Complete: Fires when all images have been loaded.
• Load: Fires on each individual image once it has been loaded.
• Scroll: Fires when the container is scrolled.

Code Revisions & Bug Fixes

None.

Discussion

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