For loops don't have to iterate one at a time. By changing our final-expression, we can count by even numbers.

We'll start at i = 0 and loop while i < 10. We'll increment i by 2 each loop with i += 2.

var ourArray = [];

for(var i = 0; i < 10; i += 2) {

  ourArray.push(i);

}

ourArray will now contain [0,2,4,6,8]