rx-js-easing
Robert Penner 的缓动函数作为 Observables。
// All easing functions take a begin value, end value, and duration (in ms).
// A few take extra arguments, which I've documented
Observable . backIn = function ( begin , end , duration , overshoot ) { } ;
Observable . backOut = function ( begin , end , duration , overshoot ) { } ;
Observable . backInOut = function ( begin , end , du
