How to create a random number between a range JavaScript

Our job is to create a function, say createRandom, that takes in two arguments and returns a pseudorandom number between the range (max exclusive).

Syntax

const createRandom = (min, max) => {
    const diff = max - min;
    const random = Math.random();
    return Math.floor((random * diff) + min);
}

Example

const min = 3;
const max = 9;
const createRandom = (min, max) => {
    const diff = max - min;
    const random = Math.random();
    return Math.floor((random * diff) + min);
}
console.log(createRandom(min, max));
console.log(createRandom(min, max));
console.log(createRandom(min, max));

6
4
8

How It Works

Understanding the algorithm:

• We take the difference of max and min to get the range size
• We create a random decimal between 0 and 1 using Math.random()
• Then we multiply the diff and random to produce random number between 0 and diff
• Then we add min to it to shift the range from [0, diff) to [min, max)
• Finally, Math.floor() converts the decimal to an integer

Alternative: Inclusive Range

To include the maximum value in the possible results:

const createRandomInclusive = (min, max) => {
    return Math.floor(Math.random() * (max - min + 1)) + min;
}

console.log(createRandomInclusive(3, 9)); // Can output 9
console.log(createRandomInclusive(3, 9));
console.log(createRandomInclusive(3, 9));

9
5
3

Comparison

Conclusion

Use Math.random() with range calculation to generate numbers within bounds. Choose between exclusive or inclusive based on your needs.