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copied!<p>Type-safe, generic version which mutates the array:</p> <pre><code>Array.prototype.rotate = (function() { // save references to array functions to make lookup faster var push = Array.prototype.push, splice = Array.prototype.splice; return function(count) { var len = this.length >>> 0, // convert to uint count = count >> 0; // convert to int // convert count to value in range [0, len) count = ((count % len) + len) % len; // use splice.call() instead of this.splice() to make function generic push.apply(this, splice.call(this, 0, count)); return this; }; })(); </code></pre> <p>In the comments, Jean raised the issue that the code doesn't support overloading of <code>push()</code> and <code>splice()</code>. I don't think this is really useful (see comments), but a quick solution (somewhat of a hack, though) would be to replace the line</p> <pre><code>push.apply(this, splice.call(this, 0, count)); </code></pre> <p>with this one:</p> <pre><code>(this.push || push).apply(this, (this.splice || splice).call(this, 0, count)); </code></pre> <hr> <p>Using <code>unshift()</code> instead of <code>push()</code> is nearly twice as fast in Opera 10, whereas the differences in FF were negligible; the code:</p> <pre><code>Array.prototype.rotate = (function() { var unshift = Array.prototype.unshift, splice = Array.prototype.splice; return function(count) { var len = this.length >>> 0, count = count >> 0; unshift.apply(this, splice.call(this, count % len, len)); return this; }; })(); </code></pre>

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