Random: getting and generating

In programming, you sometimes need to generate random numbers. They can be used to access a random array element or in other instances where uncertainty is required. JavaScript has a special Math.random() method designed for these situations. Let's get a deeper understanding of its use cases.

How to generate a random number?

The Math.random() method returns a random floating-point number between 0 (inclusive) and 1 (exclusive). This means the result will always be greater than or equal to 0 but less than 1.

Take a look at the examples below:

console.log(Math.random()); // 0.5680051955123826 
console.log(Math.random()); // 0.40357719118239643

But what if we need to generate larger random numbers, such as from 0 to 10? To solve the problem, we can simply multiply the generated values by 10 or any other number which represents the maximum value:

console.log(Math.random() * 10); // 3.4828303272733097
console.log(Math.random() * 25); // 24.893162695902227

Generating random integers

If we go even further and try to generate an integer, we will need to use another helpful method from the Math object. Math.floor() rounds a number down to the nearest integer. So, if we combine these two methods, we can write a function for our purposes:

function getRandomInteger(value) {
  return Math.floor(Math.random() * value);
}

console.log(getRandomInteger(5)); // 3
console.log(getRandomInteger(100)); // 42

Minimum and maximum values

The approach in the previous section only produces positive numbers starting from zero. Imagine a situation where we need to have different minimum and maximum boundaries or even generate negative values. At this point, we have enough knowledge to generalize these ideas and make a proper random function.

To get numbers of any range, we need to pass two arguments representing the minimum and maximum possible values to our function. You can see the function's code below with some examples of the generated values:

The below code snippet generates random numbers between two numbers:

function getRandomInteger(min, max) {
  return (Math.random() * (max - min)) + min;
}

console.log(getRandomInteger(10, 20)); // 18.648405708980263
console.log(getRandomInteger(-5, 2)); // 1.0816012391863188

The below code snippet generates random integers between two numbers:

function getRandomInteger(min, max) {
  return Math.floor(Math.random() * (max - min)) + min;
}

console.log(getRandomInteger(10, 20)); // 10
console.log(getRandomInteger(-5, 2)); // -3

The below code snippet generates random integers inclusive of the two given maximum and minimum values:

function getRandomInteger(min, max){
    return Math.floor(Math.random() * (+max + 1 - +min)) + +min;
}

console.log(getRandomInteger(10, 20)); // 15
console.log(getRandomInteger(-5, 2)); // -4
console.log(getRandomInteger(10, 20)); // 20
console.log(getRandomInteger(-5, 2)); // -5

In this example, +max and +min ensure that even if the inputs were strings, they would be converted to numbers before performing the arithmetic operations. This way, the formula correctly generates a random integer within the inclusive range of the provided min and max values.

Accessing a random array element

Now let's consider a practical problem. We have a list of rock songs, and the musicians need to decide which one to play. Choosing the first song isn't an option. So, we need to select a random element from the array.

const songs = ["Stairway to Heaven", "Imagine", "Yesterday", "Light My Fire"];

To access an array element, we use its index. This can be represented as a random integer that is less than the array's length. We already managed to produce random integers, so let's apply our knowledge to the concept of an array:

function getRandomElement(array) {
  let index = Math.floor(Math.random() * array.length);
  return array[index];
}

console.log(getRandomElement(songs)); // Imagine
console.log(getRandomElement(songs)); // Stairway to Heaven

Conclusion

In this topic, you've learned how to generate random numbers using the Math.random() method in JavaScript. You've seen how to adjust the range of random numbers, whether you need floating-point numbers or integers. You've also learned how to access random elements from an array. Remember to use Math.floor() to convert floating-point numbers to integers and ensure your range calculations are accurate.