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POpreload image with ajax
 

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    <p>Found this technique of using ajax to preload things at: <a href="http://perishablepress.com/3-ways-preload-images-css-javascript-ajax/">http://perishablepress.com/3-ways-preload-images-css-javascript-ajax/</a></p> <pre><code>window.onload = function() { setTimeout(function() { // XHR to request a JS and a CSS var xhr = new XMLHttpRequest(); xhr.open('GET', 'http://domain.tld/preload.js'); xhr.send(''); xhr = new XMLHttpRequest(); xhr.open('GET', 'http://domain.tld/preload.css'); xhr.send(''); // preload image new Image().src = "http://domain.tld/preload.png"; }, 1000); }; </code></pre> <p>I noticed that the 'ajax' preloading for this image isn't really ajax at all. It is the same as what I have been using for years already, just setting the url in a new image object's source and letting the browser load it into the cache.</p> <p>Now imagine that there was an application where, I needed to actually cancel the preloading of the image if it took over a certain amount of time. There really is no good way to do this with just setting the image to src, unlike the xhr.abort() method which stops the loading of an actual xhr request.</p> <p>Is there any reason that doing some thing like the below wouldn't preload the image just as well and allow the cancellation of the preload request?</p> <pre><code>function preload(url, timeout){ this.canceltimeout = function(){ clearTimeout(this.timeout); this.loaded = true; return false; } this.abort = function(){ this.xhr.abort(); this.aborted = true; } //creates a closure to bind the functions to the right execution scope this.$_bind = function(method){ var obj = this; return function (e){ obj[method](e);}; } //set a default of 10 second timeout if(timeout == null){ timeout = 10000; } this.aborted = false; this.loaded = false; this.xhr = new XMLHttpRequest(); this.xhr.onreadystatechange = this.$_bind('canceltimeout'); this.xhr.open('GET', url); this.xhr.send(''); this.timeout = setTimeout(this.$_bind('abort'), timeout); } var llama = new preload('/image.gif'); show_image(); function show_image(){ if(llama.loaded){ var l = new Image(); l.src = '/image.gif'; application.appendChild(l); }else if(llama.aborted){ var l = document.createElement('p'); l.innerHTML = 'image.gif got cancelled'; application.appendChild(l); }else{ setTimeout(show_image, 10); } return false; } </code></pre>
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    1. USReid Johnson
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      1. POpreload image with ajax
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      1. VTUpMod
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    1. COuse jquery man. http://api.jquery.com/jQuery.ajax/
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      1. USPatrick Lorio
    2. COcould use jquery, but that really doesn't have any bearing as to if using the xhr object to request an image is sufficent to get it loaded into the cache. Jquery is rather bulky and really doesn't help when you only need a tiny portion of it.
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      1. USReid Johnson
    3. COI see that the show_image function I posted is kinda jibberish. application is a global variable from some other javascript that I had this code tacked into to try it out. It seemed to work to, but I don't have a lot of different browsers or knowledge about their caches to pull from to see if this would work in a cross browser fashion.
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      1. USReid Johnson
 

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