MD Settings: animation interface

chrome/browser/resources/settings/animation/transition.js

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+/**
+ * @fileoverview
+ * Transitions are cancellable asynchronous state changes. A transition may
+ * compose web animations and other Transitions to manage a set of animations.
+ * Similar to Promises, they can initiate tasks after completion or
+ * cancellation.
+ */
+cr.define('settings.animation', function() {
+  'use strict';
+
+  /**
+   * Base class for modular implementations of asynchronous transitions using
+   * web animations.
+   * @constructor
+   */
+  function Transition() {}
+
+  Transition.prototype = {
+    /**
+     * If the transition is still playing, immediately finishes it and resolves
+     * |finished|.
+     */
+    finish: assertNotReached,
+
+    /**
+     * If the transition is still playing, immediately cancels it and rejects
+     * |finished|.
+     */
+    cancel: assertNotReached,
+
+    /**
+     * Sets up the transition.
+     * @protected
+     */
+    setUp: function() {
+      var cleanUp = this.cleanUp.bind(this);
+      this.finished.then(cleanUp, cleanUp);
+    },
+
+    /**
+     * Clears any temporary effects of the transition.
+     * @protected
+     */
+    cleanUp: function() {},
+
+    /** @type {Promise} */
+    finished: null,
+  };
+
+  /**
+   * Base class for instantaneous (non-animated) transitions.
+   * @constructor
+   * @extends {settings.animation.Transition}
+   */
+  function ImmediateTransition() {}

[Dan Beam, 2016/06/17 19:22:42]

i don't like this design.

the name seems like an oxymoron (many people's definition of a transition
involves a time period).

you're creating a concrete class then disabling some functionality

can we maybe make a {Step, State, Teleport, Style} have the Transition own 1-2
(end and maybe start?) instead?

[Dan Beam, 2016/06/20 23:28:03]

if you want to talk about this in a more active medium (chat, vc) possibly with
other folks (i.e. neon-animation folks, web platform folks, etc.) we can if you
want.

[michaelpg, 2016/06/28 23:17:23]

I've removed this, it hasn't been useful yet.

+
+  // ImmediateTransitions do no work outside the constructor.
+  ImmediateTransition.prototype = {
+    __proto__: Transition.prototype,
+
+    /** @final */ finish: function() {},
+    /** @final */ cancel: function() {},
+
+    /** @final */
+    finished: Promise.resolve(),
+  };
+
+  return {
+    Transition: Transition,
+    ImmediateTransition: ImmediateTransition,
+  };
+});