In JavaScript, you can use the Math. random() function to generate a pseudo-random floating number between 0 (inclusive) and 1 (exclusive).

const random = Math.random();

console.log(random);
// 0.5362036769798451

If you want to get a random number between 0 and 20, just multiply the results of Math.random() by 20:

const random = Math.random() * 20;

console.log(random);
// 15.40476356200032

To generate a random whole number, you can use the following Math methods along with Math.random():

  • Math.ceil() — Rounds a number upwards to the nearest integer
  • Math.floor() — Rounds a number downwards to the nearest integer
  • Math.round() — Rounds a number to the nearest integer

Let us use Math.floor() to round the floating number generated by Math.random() to a whole number:

const random = Math.floor(Math.random() * 20);

console.log(random);
// 12

Now we have learned that how to generate a whole random number, let us write a function that takes in an integer as input and returns a whole number between 0 and the integer itself:

const random = (max = 50) => {
    return Math.floor(Math.random() * max);
};

console.log(random(100));
// 66

To generate a random number between two specific numbers (min included, max excluded), we have to update the random() method like below:

const random = (min = 0, max = 50) => {
    let num = Math.random() * (max - min) + min;

    return Math.floor(num);
};

console.log(random(10, 40));
// 28

In the above code, we used (max - min) + min to avoid cases where the max number is less than the min number.

To generate a random number that includes both min and max values, just change Math.floor() to Math.round():

const random = (min = 0, max = 50) => {
    let num = Math.random() * (max - min) + min;

    return Math.round(num);
};

console.log(random(10, 70));
// 51

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