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97 lines
3.7 KiB
97 lines
3.7 KiB
/**
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* @class Images
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* This class loads images and keeps them stored.
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*/
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function Images(callback) {
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this.images = {};
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this.imageBroken = {};
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this.callback = callback;
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}
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/**
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* @param {string} url The Url to cache the image as
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* @return {Image} imageToLoadBrokenUrlOn The image object
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*/
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Images.prototype._addImageToCache = function (url, imageToCache) {
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// IE11 fix -- thanks dponch!
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if (imageToCache.width === 0) {
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document.body.appendChild(imageToCache);
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imageToCache.width = imageToCache.offsetWidth;
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imageToCache.height = imageToCache.offsetHeight;
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document.body.removeChild(imageToCache);
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}
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this.images[url] = imageToCache;
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}
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/**
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* @param {string} url The original Url that failed to load, if the broken image is successfully loaded it will be added to the cache using this Url as the key so that subsequent requests for this Url will return the broken image
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* @param {string} brokenUrl Url the broken image to try and load
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* @return {Image} imageToLoadBrokenUrlOn The image object
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*/
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Images.prototype._tryloadBrokenUrl = function (url, brokenUrl, imageToLoadBrokenUrlOn) {
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//Store the instance of the Images object so that we can reference it in events
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var self = this;
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//If any of the parameters aren't specified then exit the function because nothing constructive can be done
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if (url === undefined || brokenUrl === undefined || imageToLoadBrokenUrlOn === undefined) return;
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//Clear the old subscription to the error event and put a new in place that only handle errors in loading the brokenImageUrl
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imageToLoadBrokenUrlOn.onerror = function() {
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console.error("Could not load brokenImage:", brokenUrl);
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//Add an empty image to the cache so that when subsequent load calls are made for the url we don't try load the image and broken image again
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self._addImageToCache(url, new Image());
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};
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//Set the source of the image to the brokenUrl, this is actually what kicks off the loading of the broken image
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imageToLoadBrokenUrlOn.src = brokenUrl;
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}
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/**
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* @return {Image} imageToRedrawWith The images that will be passed to the callback when it is invoked
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*/
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Images.prototype._redrawWithImage = function (imageToRedrawWith) {
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if (this.callback) {
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this.callback(imageToRedrawWith);
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}
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}
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/**
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* @param {string} url Url of the image
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* @param {string} brokenUrl Url of an image to use if the url image is not found
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* @return {Image} img The image object
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*/
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Images.prototype.load = function (url, brokenUrl, id) {
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//Store the instance of the Images object so that we can reference it in events
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var self = this;
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//Try and get the image from the cache, if successful then return the cached image
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var cachedImage = this.images[url];
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if (cachedImage) return cachedImage;
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//Create a new image
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var img = new Image();
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//Subscribe to the event that is raised if the image loads successfully
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img.onload = function() {
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//Add the image to the cache and then request a redraw
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self._addImageToCache(url, img);
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self._redrawWithImage(img);
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};
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//Subscribe to the event that is raised if the image fails to load
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img.onerror = function () {
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console.error("Could not load image:", url);
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//Try and load the image specified by the brokenUrl using
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self._tryloadBrokenUrl(url, brokenUrl, img);
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}
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//Set the source of the image to the url, this is actuall what kicks off the loading of the image
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img.src = url;
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//Return the new image
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return img;
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};
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module.exports = Images;
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