JavaScript - Difference between random function results

Math.random() produces floating point values in the interval [0, 1) (from zero inclusive to one exclusive). This means that there is a slight difference between the two approaches:

Math.ceil(Math.random() * x) will produce integers in the interval [0, x] (from zero inclusive to x inclusive). This is because Math.ceil(0) will return a zero. Although the chance of getting that is extremely small.

function minRandom() { return 0; }
function maxRandom() { return 0.9999999; }

const x = 10;
console.log("min:", Math.ceil(minRandom() * x));
console.log("max:", Math.ceil(maxRandom() * x));

Math.floor(Math.random() * x) + 1 will produce integers in the interval [1, x] (from one inclusive to x inclusive). This is because Math.floor(Math.random() * x) itself produces integers in the interval [0, x-1] (zero inclusive to x-1 inclusive).

function minRandom() { return 0; }
function maxRandom() { return 0.9999999; }

const x = 10;
console.log("min:", Math.floor(minRandom() * x) + 1);
console.log("max:", Math.floor(maxRandom() * x) + 1);

Yes, there's a difference.

There is a chance, albeit a very very small one, that the second version could unexpectedly return zero.

This happens if Math.random() itself returns exactly 0.0, which it legally can.