How to generate a random number between a range in JavaScript
In JavaScript, the Math.random function will generate a random floating point number between 0 and 1(0 is included 1 is excluded):
Math.random();
Generate a random number with a Max limit
Let’s say we need to generate a random number under 100. To do this, we would multiply the random number by 100. Math.random() will not return 1, so the value will be below 100.
Math.random() * 100; // 84.06448370345245
We can use Math.floor to round it down as shown here:
function generateRandom(maxLimit = 100){let rand = Math.random() * maxLimit;console.log(rand); // say 99.81321410836433rand = Math.floor(rand); // 99return rand;}generateRandom(); // 43generateRandom(500); // 165
Generate a random number between two numbers
In this case, we will have a MIN and a MAX value and will need to include the MIN value and exclude the MAX value.
If the MIN value is always 0, then we can multiply the random number with the MAX value, but if the MIN value is other than 0, we need to find the difference between MAX and MIN. Then we will multiply the random number with that difference and add the MIN value.
- Let’s say
MIN = 3&MAX = 5. - Difference is
MAX - MIN = 2. - Upon multiplying a random number by 2, we will get a value between 0 and below 2. So, the possible value will be either 0 or 1.
- When we add the
MIN(3)value to the random number, the result is either3or4. We can see this as follows:
function generateRandom(min = 0, max = 100) {// find difflet difference = max - min;// generate random numberlet rand = Math.random();// multiply with differencerand = Math.floor( rand * difference);// add with min valuerand = rand + min;return rand;}console.log(generateRandom());
The above can be also be written as:
const random = (min, max) => Math.floor(Math.random() * (max - min)) + min;
