So, I implemented a small testcode and found out, that we both were wrong 😉
For two integers "min" and "max" (including both) I get a good eval distribution of integer random numbers with this function:
Math.floor(Math.random()*(max+1)+min);
Mozilla docs show a slightly different variant:
Math.floor(Math.random() * (max - min + 1)) + min;
which seams to give the same results. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/random