gistfile1.js

function bench (fn) {
        var t1 = Date.now();
        for (var i = 0; i < 10000000; i++) {
                fn();
        }
        var t2 = Date.now();
        console.log(t2 - t1);
}

var fn1 = function() {
        var i = '1' + '2' + '3';
}

var fn2 = function() {
        var i = '1';
        i += '2';
        i += '3';
}

bench(fn1);
bench(fn2);
/*
* BVadim from habr
*/