let Phi = (1 + Math.sqrt(5)) / 2;

  let phi = (1 - Math.sqrt(5)) / 2;

  return Math.floor((Math.pow(Phi, n) - Math.pow(phi, n)) / Math.sqrt(5));

}

​

let i = 0;

let sum = 0;

​

while (true) {

  let f = fibonacci(i);

  if (f % 2 == 0) {

    sum += f;

  }

  if (fibonacci(i + 1) >= 4000000) {

    break;

  } else {

    i++;

  }

}

​

console.log(sum);