在javascript中重现android的onfling事件

I want to reproduce android's fling event in javascript.What I don't understand is what type of mathematical function I have to use.I know that I have to calculate how many pixels the mouse is been moved in a specific time and do the fling animation based on this but I don't know how to do this in javascript.I have to do the fling animation based on the last velocity(pixel/time) i have found?Or I have to do the fling animation based on all the velocity I have found?And what type of method I have to use to find the velocity ?I want to reproduce android's fling event in ja