A useful javascript profiling function ...

timeit.js

    // f(N) is run a few times, timed and some stats are
    // returned as an object.
    function timeit(f, N) {
        var start, stop, dt;
        var worst = 0, best = 1000 * 3600, mean = 0, sigma = 0;
        var i, M = 7;
        for (i = 0; i < M; ++i) {
            start = Date.now();
            f(N);
            stop = Date.now();
            dt = stop - start;
            best = Math.min(best, dt);
            worst = Math.max(worst, dt);
            mean += dt;
            sigma += dt * dt;
        }

        mean /= M;
        sigma /= M;

        return { best: best, worst: worst, mean: mean, spread: Math.sqrt(sigma - mean * mean) };
    }