console.time('a');

var LIMIT = 4000000,
    x = [1, 2],
    s = 2;

while (true) {
    var l = x.length,
        fib = x[l - 1] + x[l - 2];

    if (fib > LIMIT)
        break;

    x.push(fib);

    if (fib % 2 == 0)
        s += fib;
}

console.log(s);

console.timeEnd('a');