Add transition.end. Fixes #77.

.eslintrc

@@ -1,6 +1,9 @@
 parserOptions:
     sourceType: module
 
+env:
+    es6: true
+
 extends:
     "eslint:recommended"
 

src/transition/end.js

@@ -0,0 +1,9 @@
+// TODO Anonymous names for event listeners.
+export default function() {
+  var that = this, size = that.size();
+  return new Promise(function(resolve, reject) {
+    that.on("cancel.end interrupt.end", reject).on("end.end", function() {
+      if (--size === 0) resolve();
+    });
+  });
+}

src/transition/index.js

@@ -16,6 +16,7 @@ import transition_styleTween from "./styleTween";
 import transition_text from "./text";
 import transition_transition from "./transition";
 import transition_tween from "./tween";
+import transition_end from "./end";
 
 var id = 0;
 
@@ -60,5 +61,6 @@ Transition.prototype = transition.prototype = {
   tween: transition_tween,
   delay: transition_delay,
   duration: transition_duration,
-  ease: transition_ease
+  ease: transition_ease,
+  end: transition_end
 };