https://projecteuler.net/problem=2

fib

var fib = [1,2] , i=0;j=1 , index=2 , sum=2;


while ( fib[j]<4*Math.pow(10,6) ){
 fib[index] = fib[i]+fib[j];
 if (4*Math.pow(10,6)<=fib[index]) {
   break;
 }
 if ( !(fib[index]%2) )
   sum+=fib[index];
   index++;
   i++;
   j++;
}

console.log(sum)