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POHow to detect onload event of image which was loaded in custom object
 

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  1. POHow to detect onload event of image which was loaded in custom object
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    <p>I am creating a sample program to display an image on canvas but would like to enclose actual drawing process into a custom object.</p> <p>The following code won't show the image as <b>pictFrame.img.onload</b> can't catch onload event of image file. Chrome console says "TypeError: Cannot set property 'onload' of undefined" with the expression although it can correctly evaluate <b>pictFrame.img.src</b> or <b>pictFrame.img.height</b>.</p> <p>How should I detect image loading which is being initiated when the object is created?</p> <pre><code>&lt;html&gt; &lt;head&gt; &lt;script type="text/javascript"&gt; function pictFrame(context, imgsrc, pos_x, pos_y, size_x, size_y) { this.context = context; this.img = new Image(); this.img.src = imgsrc; this.pos_x = pos_x; this.pos_y = pos_y; this.size_x = size_x; this.size_y = size_y; this.draw = function() { this.context.drawImage(this.img, this.pos_x, this.pos_y, this.size_x, this.size_y); }; } // These variables must live while the page is being displayed. // Therefore, they can't be defined within window.onload function. var canvas; var context; var pictFrame; window.onload = function() { canvas = document.getElementById("canvas"); context = canvas.getContext("2d"); pictFrame = new pictFrame(context, "darwin.jpg", 10, 10, 200, 200); }; pictFrame.img.onload = function() // Can't catch onload event { pictFrame.draw(); } &lt;/script&gt; &lt;/head&gt; &lt;body&gt; &lt;canvas id="canvas" width="500" height="300"&gt;&lt;/canvas&gt; &lt;/body&gt; &lt;/html&gt; </code></pre>
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