| // Copyright 2012 The Closure Library Authors. All Rights Reserved. |
| // |
| // Licensed under the Apache License, Version 2.0 (the "License"); |
| // you may not use this file except in compliance with the License. |
| // You may obtain a copy of the License at |
| // |
| // http://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, software |
| // distributed under the License is distributed on an "AS-IS" BASIS, |
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| // See the License for the specific language governing permissions and |
| // limitations under the License. |
| |
| /** |
| * @fileoverview Simple image loader, used for preloading. |
| * @author nnaze@google.com (Nathan Naze) |
| */ |
| |
| goog.provide('goog.labs.net.image'); |
| |
| goog.require('goog.Promise'); |
| goog.require('goog.events.EventHandler'); |
| goog.require('goog.events.EventType'); |
| goog.require('goog.net.EventType'); |
| goog.require('goog.userAgent'); |
| |
| |
| /** |
| * Loads a single image. Useful for preloading images. |
| * |
| * @param {string} uri URI of the image. |
| * @param {(!Image|function(): !Image)=} opt_image If present, instead of |
| * creating a new Image instance the function will use the passed Image |
| * instance or the result of calling the Image factory respectively. This |
| * can be used to control exactly how Image instances are created, for |
| * example if they should be created in a particular document element, or |
| * have fields that will trigger CORS image fetches. |
| * @return {!goog.Promise<!Image>} A Promise that will be resolved with the |
| * given image if the image successfully loads. |
| */ |
| goog.labs.net.image.load = function(uri, opt_image) { |
| return new goog.Promise(function(resolve, reject) { |
| var image; |
| if (!goog.isDef(opt_image)) { |
| image = new Image(); |
| } else if (goog.isFunction(opt_image)) { |
| image = opt_image(); |
| } else { |
| image = opt_image; |
| } |
| |
| // IE's load event on images can be buggy. For older browsers, wait for |
| // readystatechange events and check if readyState is 'complete'. |
| // See: |
| // http://msdn.microsoft.com/en-us/library/ie/ms536957(v=vs.85).aspx |
| // http://msdn.microsoft.com/en-us/library/ie/ms534359(v=vs.85).aspx |
| // |
| // Starting with IE11, start using standard 'load' events. |
| // See: |
| // http://msdn.microsoft.com/en-us/library/ie/dn467845(v=vs.85).aspx |
| var loadEvent = (goog.userAgent.IE && goog.userAgent.VERSION < 11) ? |
| goog.net.EventType.READY_STATE_CHANGE : goog.events.EventType.LOAD; |
| |
| var handler = new goog.events.EventHandler(); |
| handler.listen( |
| image, |
| [loadEvent, goog.net.EventType.ABORT, goog.net.EventType.ERROR], |
| function(e) { |
| |
| // We only registered listeners for READY_STATE_CHANGE for IE. |
| // If readyState is now COMPLETE, the image has loaded. |
| // See related comment above. |
| if (e.type == goog.net.EventType.READY_STATE_CHANGE && |
| image.readyState != goog.net.EventType.COMPLETE) { |
| return; |
| } |
| |
| // At this point, we know whether the image load was successful |
| // and no longer care about image events. |
| goog.dispose(handler); |
| |
| // Whether the image successfully loaded. |
| if (e.type == loadEvent) { |
| resolve(image); |
| } else { |
| reject(null); |
| } |
| }); |
| |
| // Initiate the image request. |
| image.src = uri; |
| }); |
| }; |