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    <p>Using <code>cancelAnimationFrame</code> <em>alone</em> won't necessary stop the animation loop (it turns out).</p> <p>To be absolute sure you will need to use a <em>conditional check</em> as well - a generic example:</p> <pre><code>var isPlaying; /// our condition function loop() { /* funky stuff here */ If (isPlaying === true) requestId = requestAnimationFrame(loop); } </code></pre> <p>Then starting it:</p> <pre><code>functiom start() { isPlaying = true; loop(); } </code></pre> <p>Now when you want to stop the animation you need to do:</p> <pre><code>function stop() { isPlaying = false; /// kill any request in progress if (requestId) cancelAnimationFrame(requestId); } </code></pre> <p>If you don't do this you risk stacking calls to the loop - for example:</p> <p>If you resize and cAF isn't stopping rAF from re-trigger the loop, the old loop will still run in the background and you will start a new loop on top of that.</p> <p>That is why you see speed increases as the old and the new loop will both increment the positions before the stars are drawn to screen.</p> <p>On the third re-size yet another loop is started, and eventually the whole thing will block the browser.</p> <h1>However</h1> <p>Instead of utilizing start and stop of the loop I would recommend you the following approach:</p> <ul> <li>Create canvas once</li> <li>Start the loop only once</li> <li>In this case, a re-factoring of the whole re-size mechanism could be beneficial (for instance, separate needed initializations (width and height of element) from first time initializations that can be re-used later).</li> <li>There is no need to re-init the stars for each re-size as you will use the width and height to check their boundaries (canvas will do the clipping).</li> </ul> <p>When resizing you <em>can</em> consider using a conditional flags to prevent <em>render</em> while re-sizing.</p> <p>Although generally, a condition to block rendering while canvas changes size is really not necessary due to the single-thread nature of JavaScript and in cases such as this you do boundary check on current element size. Canvas itself will take care of the clipping for you.</p> <p>And that being said: there should be no need to <em>re-create</em> the canvas element each time.</p> <p>This creates an unnecessary overhead. Simple set new width and height on its properties if canvas is already created:</p> <pre><code>if (typeof canvas === 'undefined') canvas = /* only create if it doesn't exist */ canvas.width = width; canvas.height = height; </code></pre> <p>PS: <strong><a href="http://codepen.io/anon/pen/CLKhn" rel="nofollow">I "hampered" a version with some brute-force-ish implementations</a></strong> of the above. It's far from complete or of high quality but takes out some of the pain for the sake of example to give you a couple of pointers.</p> <p>Please adopt to suit your needs.</p> <p><strong>Update</strong>:</p> <p>To include more info from the additional comments:</p> <p>when a new size is set on a canvas element its <em>context</em> is reset to default (<code>fillStyle</code> becomes transparent, <code>strokeStyle</code> black, transform is reset and so on).</p> <p>This means that all non-default settings must be set again after each new size is set.</p> <p>Setting a new size may (and typically do) clear the content of the canvas as well so that all pixels becomes transparent black.</p>
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    1. POWhy is animation speed increasing each time the target element is deleted and recreated?
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    1. COThis is the sort of answer that makes SO great. Thanks for helpin' me learn.
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    2. COI updated my pen to reflect some changes you suggested (refactoring, especially). I discovered, though, that your code wasn't actually resizing the canvas (though it seems to be doing so in codepen, for some reason), which was a no-go. Resizing the canvas resets the canvas, so whenever I updated its dimensions, I lost all the stars. The new code resets the position of the stars proportionally to the dimensions as they update.
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