Question

So I use such script for random int generation inside of range

function randomInRange(start, end)
{
  if ((start >= 0) && (end >= 0))
  {
    return Math.round(Math.abs(start) + (Math.random() * (Math.abs(end) - Math.abs(start))));

  }
  else if ((start <= 0) && (end <= 0))
  {
    return 0 - (Math.round(Math.abs(start) + (Math.random() * (Math.abs(end) - Math.abs(start)))));
  }
  else
  {
    return Math.round(((start) + Math.random() * (end - start)));
  }

}

You can see it at work here. for Positive ranges its correct, for negative its correct but I get bad and wrong results for mixed. Why and how to fix it?

I try to use formula like Math.round(start + Math.random() * (end - start));

Answer 1

OK, I found the problem, you’re performing algebra on strings (since in your code $('fnt').value is the value of an input box, which is a string), not numbers, so things like + will end up concatenating strings and not adding their numeric content. In your particular example, you have:

Math.round(((start) + Math.random() * (end - start)))

Which evaluates to:

Math.round((('13') + Math.random() * ('-666' - '13'))) 

Which evaluates to (for example):

Math.round("13-339.44615370430984")

Since '13' + '-339.44615370430984' will be concatenated, and finally the Math.round call will return NaN

You should have:

function randomInRange(start, end) {
  start = Number(start); end = Number(end);
  return Math.round(start + Math.random() * (end - start));
}

Or change the values you pass into the function, making sure they’re numbers.