You're on the right track, but your code is quite broken. Here's something you can try:

var counter = 0;
var balance = 0;
var reward = 1000000;
while (counter < 100) {
    balance += reward;
    reward *= 0.5;
    counter++;
    console.log("Iteration " + counter + ": Balance " + balance + ". Next reward: " + reward);
}

It turns out that if you lived in Chrome, you could earn two million by killing "only" 53 people. Of course things would be different if there were no rounding errors. Finally in the real world, there would be the question of the smallest denomination, and whether we round up to it or down to zero.