Alternative iteration loops for large arrays

iterate.large.js

//The book Speed Up Your Site (New Riders) introduced a version of Duff’s Device in JavaScript that moves the processing of the extra array items outside the main loop, allowing the switch statement to be removed and resulting in an even faster way of processing a large number of items:

var iterations = Math.floor(values.length / 8);
var leftover = values.length % 8;
var i = 0;

if (leftover > 0){
    do {
        process(values[i++]);
    } while (--leftover > 0);
}

do {
    process(values[i++]);
    process(values[i++]);
    process(values[i++]);
    process(values[i++]);
    process(values[i++]);
    process(values[i++]);
    process(values[i++]);
    process(values[i++]);
} while (--iterations > 0);
//Duff’s Device, and the modified version presented here, is useful primarily with large arrays. For small arrays, the performance gain is minimal compared to standard loops. Therefore, you should attempt to use Duff’s Device only if you notice a performance bottleneck relating to a loop that must process a large number of items.