euler_2.js

var a = 1,
    b = 2,
    temp = 0,
    total = 2;

while (total < 4000001) {

   temp = a + b; 
   
   if (temp%2 === 0) {
     total += temp;
   }
   
   a = b;
   b = temp;

}

console.log(total);