JavaScript Preloader for HTML5 Apps : PxLoader

PxLoader is a Javascript library that helps you download images, sound files or anything else you need before you take a specific action on your site (like showing a user interface or starting a game). You can use it to create a preloader for HTML5 games and websites.

It let's you monitor download status by providing progress and completed events and it lets you prioritize the order in which items are downloaded. You can even tag groups of files and then prioritize downloads or register for events by tag.