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function shake(e, oncomplete, distance, time) {
    // Handle arguments
    if (typeof e === "string") e = document.getElementById(e);
    if (!time) time = 500;
    if (!distance) distance = 5;
    var originalStyle = e.style.cssText;      // Save the original style of e
    e.style.position = "relative";            // Make e relatively positioned
    var start = (new Date()).getTime();       // Note the animation start time
    animate();                                // Start the animation
    // This function checks the elapsed time and updates the position of e.
    // If the animation is complete, it restores e to its original state.
    // Otherwise, it updates e's position and schedules itself to run again.
    function animate() {
        var now = (new Date()).getTime();     // Get current time
        var elapsed = now-start;              // How long since we started
        var fraction = elapsed/time;          // What fraction of total time?
        if (fraction < 1) {     // If the animation is not yet complete
            // Compute the x position of e as a function of animation
            // completion fraction. We use a sinusoidal function, and multiply
            // the completion fraction by 4pi, so that it shakes back and
            // forth twice.
            var x = distance * Math.sin(fraction*4*Math.PI);
            e.style.left = x + "px";
            // Try to run again in 25ms or at the end of the total time.
            // We're aiming for a smooth 40 frames/second animation.
            setTimeout(animate, Math.min(25, time-elapsed));
        }
        else {                  // Otherwise, the animation is complete
            e.style.cssText = originalStyle  // Restore the original style
            if (oncomplete) oncomplete(e);   // Invoke completion callback
        }
    }
}