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JavaScript image preloader with callback
/*
* Copyright (C) 2012 Eike Send
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to
* deal in the Software without restriction, including without limitation the
* rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
* sell copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
* IN THE SOFTWARE.
*/
function imgpreload( imgs, callback ) {
"use strict";
var loaded = 0;
var images = [];
imgs = Object.prototype.toString.apply( imgs ) === '[object Array]' ? imgs : [imgs];
var inc = function() {
loaded += 1;
if ( loaded === imgs.length && callback ) {
callback( images );
}
};
for ( var i = 0; i < imgs.length; i++ ) {
images[i] = new Image();
images[i].onabort = inc;
images[i].onerror = inc;
images[i].onload = inc;
images[i].src = imgs[i];
}
}
@eikes
Owner
eikes commented Oct 20, 2012

Example usage:

imgpreload(["rainbow.png"], function( images ) {
  canvas.drawImage( images[0], 0, 0 );
});
@DimitarChristoff

in inc on line 28, add this.onload = this.onabort = this.onerror = null to clear the handlers. eg. use case: IE6/7 and animated gif, they fire onload on every animation loop.

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