Is there a difference between the results of Math.floor(Math.random() * x) + 1 and Math.ceil(Math.random() * x)?
2 Answers
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);Comments
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.
3 Comments
VLAZ
I'm not really sure it's unexpected. Well, unless you never wanted a zero. But it's a totally valid output.
Alnitak
@VLAZ kinda - it's certainly valid, but it might surprise some people (including some of the other commentators here).
VLAZ
¯\_(ツ)_/¯ Any output can be a surprise if you don't know how something works.
Math.random() * xis a integer they will have different values. However, the chance of that is small.0and the second can.Math.floor(0 + 1) == 1, butMath.ceil(0) == 0