benchmark.js

var benchmark = function(callback) {
    var max = 1000000;
    var start = Date.now();

    for (var i = 0; i < max; ++i) {
        callback();
    }

    var end = Date.now();

    return end - start;
};


var f = function() {
    var a = 1 + 1;    
}

console.log(benchmark(f));