Javascript random addition and subtraction generator that prevents running negative numbers

On my miniquest to improve my Javascript, I'm building some quick games that are designed to not take long to code. I have a timed add/sub like so:

function flash() {

      size = 3
      rand1 = Math.floor((Math.random() * 201) - 100);
      rand2 = Math.floor((Math.random() * 201) - 100);
      randMax = Math.max(rand1,rand2)
      randMin = Math.min(rand1,rand2)

      if (randMax - randMin > 0 ){
      if (i < size) {

        timer = setTimeout(function() {
          display.value = randMax;
          answer += randMax;
          setTimeout(function() {
            display.value = '';
          }, 1000);
          flash();
        }, 5000);
        i++;
      }} else {
        clearTimeout(timer);
      }
    }

To prevent a negative answer for both the final result AND any on-the-fly result, is the only way to populate the answer in an array beforehand, and compare max/min as we iterate through the array? (eg. [1,-3,4,1,8] would fail 'always >= 0' parameters, while [1,-1,3,-2,4] would pass. If so/if not, how would you approach it?