event_suspender.js revision cedac228d2dd51db4b79ea1e72c7f249408ee061 
1// Copyright 2014 The Chromium Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5/**
6 * @fileoverview Allows events to be suspended.
7 *
8 */
9
10goog.provide('cvox.ChromeVoxEventSuspender');
11
12/**
13 * @namespace
14 */
15cvox.ChromeVoxEventSuspender = function() {};
16
17/**
18 * A nestable variable to keep track of whether events are suspended.
19 *
20 * @type {number}
21 * @private
22 */
23cvox.ChromeVoxEventSuspender.suspendLevel_ = 0;
24
25/**
26 * Enters a (nested) suspended state.
27 */
28cvox.ChromeVoxEventSuspender.enterSuspendEvents = function() {
29  cvox.ChromeVoxEventSuspender.suspendLevel_ += 1;
30}
31
32/**
33 * Exits a (nested) suspended state.
34 */
35cvox.ChromeVoxEventSuspender.exitSuspendEvents = function() {
36  cvox.ChromeVoxEventSuspender.suspendLevel_ -= 1;
37}
38
39/**
40 * Returns true if events are currently suspended.
41 *
42 * @return {boolean} True if events are suspended.
43 */
44cvox.ChromeVoxEventSuspender.areEventsSuspended = function() {
45  return cvox.ChromeVoxEventSuspender.suspendLevel_ > 0;
46};
47
48/**
49 * Returns a function that runs the argument with all events suspended.
50 *
51 * @param {Function} f Function to run with suspended events.
52 * @return {?} Returns a function that wraps f.
53 */
54cvox.ChromeVoxEventSuspender.withSuspendedEvents = function(f) {
55  return function() {
56    cvox.ChromeVoxEventSuspender.enterSuspendEvents();
57    var ret = f.apply(this, arguments);
58    cvox.ChromeVoxEventSuspender.exitSuspendEvents();
59    return ret;
60  };
61};
62
63/**
64 * Returns a handler that only runs the argument if events are not suspended.
65 *
66 * @param {Function} handler Function that will be used as an event handler.
67 * @param {boolean} ret Return value if events are suspended.
68 * @return {Function} Function wrapping the handler.
69 */
70cvox.ChromeVoxEventSuspender.makeSuspendableHandler = function(handler, ret) {
71  return function() {
72    if (cvox.ChromeVoxEventSuspender.areEventsSuspended()) {
73      return ret;
74    }
75    return handler();
76  };
77};
78