AS3GIF lets you play and encode animated GIF's with ActionScript 3 Since web pages can usually natively play GIFs fine, it's only a port of the GIFEncoder portions of the library. But there are some ...

Well, that doesn't exist in Javascript (natively, anyway) so instead, I use what I feel is a decent analogue: the canvas context. However, if you're in a situation where you don't have a real <canvas> ...