wrap finish event as promise

src/lib/MotionEngine.js

@@ -27,9 +27,10 @@ class MotionEngine {
         }
 
         // a = {o-object, a-attributes, t-time, f-finish event, d-delay, m-mode, r-repeat, 
-        // rd-repeat the delay, rf-reset on finish, u-on update, s-scope}
+        // rd-repeat the delay, rf-reset on finish, u-on update, s-scope, p-promise on finish}
         this.add = function (a) {
             a = Array.isArray(a) ? a : [a];
+            let r = [];
             a.forEach(e => {
                 if (e.t == 0){
                     e.t = 1;
@@ -37,7 +38,11 @@ class MotionEngine {
                 }else{
                     aq.push(e);
                 }
+                if (e.p && !e.f){
+                    r.push(new Promise( resolve=> e.f = resolve ))
+                }
             });
+            if (r.length) return Promise.all(r);
         };
 
         this.clear = function (object, reset = false) {