"Why would you make a responsive grid in js and not just use a few lines of css grid?"

If you want to add a little more dynamics to your grid, this is for you because this library provides a quick way to add new items, make random grids, filtering, even background effects.
EasyGrid makes it faster and more efficient because it does basically everything for you...and the best part is that it is dependency-free (JS and CSS).

"Why i need this when i have a css framework?"

It is not meant to replace any CSS Framework, in fact, works even better when both are combined.

"Can i do filtering with this library?"

Yes, the latest version of EG allows you to make filtering. Check demo page for a sneak peak of what you can do.