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// 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.events.EventHandler');
goog.require('goog.events.EventType');
goog.require('goog.net.EventType');
goog.require('goog.result.SimpleResult');
goog.require('goog.userAgent');
/**
* Loads a single image. Useful for preloading images. May be combined with
* goog.result.combine to preload many 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.result.Result} An asyncronous result that will succeed
* if the image successfully loads or error if the image load fails.
*/
goog.labs.net.image.load = function(uri, opt_image) {
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. Instead, we 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
var loadEvent = goog.userAgent.IE ? goog.net.EventType.READY_STATE_CHANGE :
goog.events.EventType.LOAD;
var result = new goog.result.SimpleResult();
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) {
result.setValue(image);
} else {
result.setError();
}
});
// Initiate the image request.
image.src = uri;
return result;
};
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