Test functions to show that accessing Math as a global is much slower than if it were local.

global-access.js

function f1(N) {
    var i, sum = 0;
    for (i = 0; i < N; ++i) {
        sum += Math.sin(i);
    }
    return sum;
}

function f2(f) {
    return function (N) {
        var i, sum = 0;
        for (i = 0; i < N; ++i) {
            sum += f(i);
        }
        return sum;
    };
}

function f3(Module) {
    return function (N) {
        var i, sum = 0;
        for (i = 0; i < N; ++i) {
            sum += Module.sin(i);
        }
        return sum;
    };
}

// 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) };
}

1. In Chrome, f1(N) takes about twice as much time as f2(Math.sin)(N) which is comparable in speed to f3(Math)(N).
2. The functions don't differ much in speed on Safari, which runs all of them at around 2x speed compared to the f1(N) in Chrome.

Original post on this performance characteristic of V8 - https://plus.google.com/102694714835839603248/posts/i9dahgLDs9w

Macbook Air 1.7GHz Core i5 / 4GB / Lion
N = 100M and reporting only 2 significant figures

Chrome [15.0.849.1 dev]: f1local = 23 secs, f2local = 13 secs
Safari [5.1 (7534.48.3)]: f1local = 8.6 secs, f2local = 8.6 secs
Firefox [6.0]: f1local = 13 secs, f2local = 12 secs

Intel(R) Core(TM)2 Quad CPU Q6600 @ 2.40GHz 4GB RAM Windows Vista

N = 100M; 23 sec in FF 6.0.2 (f1local)
N = 100M; 17 sec in FF 6.0.2 (f2local)

N = 100M; 28 sec in Safari 5.1 (7534.50) (f1local)
N = 100M; 13 sec in Safari 5.1 (7534.50) (f2local)

N = 100M; 45 sec in Chrome 14.0.835.163 beta-m (f1local)
N = 100M; 15 sec in Chrome 14.0.835.163 beta-m (f2local)

(Thanks Bharat!)