MD Bookmarks: Scroll and select items that are added to the main list

chrome/browser/resources/md_bookmarks/timer_proxy.js

 // Copyright 2017 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 A class that mediates window timer calls to support mockability
  * in tests.
  */
 
 cr.define('bookmarks', function() {
   /** @constructor */
   function TimerProxy() {}
 
   TimerProxy.prototype = {
     /**
      * @param {Function|string} fn
      * @param {number=} delay
      * @return {number}
      */
     setTimeout: function(fn, delay) {
       return window.setTimeout(fn, delay);
     },
 
     /** @param {number|undefined?} id */
     clearTimeout: function(id) {
       window.clearTimeout(id);
     },
   };
 
+  /**
+   * A timer which will fire on the next task after the last time it is reset.

[calamity, 2017/07/26 05:36:06]

nit: This isn't strictly true. It gets added to the task list each time, so the
last reset can have a bunch of tasks between itself and the actual callback
firing.

How about:

A one-shot debouncer which fires the given callback after a delay. The delay can
be refreshed by calling resetTimer. Resetting with no delay moves the callback
to the end of the task queue.

[tsergeant, 2017/07/26 06:34:07]

Done.

+   * @param {function()} callback
+   * @constructor
+   */
+  function Debouncer(callback) {

[tsergeant, 2017/07/25 00:13:00]

I'm happy enough with this for now, but one unanswered question is how we make
this testable, both in terms of getting a 'TestDebouncer' instance, and how we
inject a TestTimerProxy into it.

[calamity, 2017/07/26 05:36:06]

Acknowledged.

+    this.callback_ = callback;
+    this.timerProxy_ = new TimerProxy();
+    this.timer_ = null;
+    this.boundTimerCallback_ = this.timerCallback_.bind(this);
+    this.isDone_ = false;
+    this.promiseResolver_ = new PromiseResolver();

[calamity, 2017/07/26 05:36:06]

nit: Couple of types?

[tsergeant, 2017/07/26 06:34:07]

Done.

+  }
+
+  Debouncer.prototype = {
+    resetTimer: function() {

[calamity, 2017/07/26 05:36:06]

nit: resetTimeout perhaps? This will be given a delay param in my auto expander
patch. (Or just do it now to align with the class comment I suggested)

[tsergeant, 2017/07/26 06:34:07]

Done.

+      if (this.timer_)
+        this.timerProxy_.clearTimeout(this.timer_);
+      this.timer_ = this.timerProxy_.setTimeout(this.boundTimerCallback_);
+    },
+
+    /**
+     * @return {boolean} True if the Debouncer has finished processing.
+     */
+    done: function() {
+      return this.isDone_;
+    },
+
+    /**
+     * @return {Promise} Promise which resolves immediately after the callback.
+     */
+    get promise() {
+      return this.promiseResolver_.promise;
+    },
+
+    /** @private */
+    timerCallback_: function() {
+      this.isDone_ = true;
+      this.callback_.call();
+      this.promiseResolver_.resolve();
+    },
+  };
+
   return {
+    Debouncer: Debouncer,
     TimerProxy: TimerProxy,
   };
 });