求个大神能为这个代码加下注解，尽量详细些

function chainAnimationsPromise(elem, animations) { let ret = null; let p = currentPromise; for(const anim of animations) { p = p.then(function(val) { ret = val; return anim(elem); }) } return p.catch(function(e) { /* ignore and keep going */ }).then(function() { return ret; }); }