Cookbooks
TypeScript
Chapter 3. Numbers
Generating random numbers

TypeScript:
Generating random numbers

How to:

In TypeScript, you can generate random numbers using the global Math object. Below are some practical examples demonstrating how to produce random numbers for different requirements.

Generating a Basic Random Number

To generate a basic random decimal number between 0 (inclusive) and 1 (exclusive), you use Math.random(). This does not require any additional manipulation:

const randomNumber = Math.random();
console.log(randomNumber);

This might output a value like 0.8995452185604771.

Generating a Random Integer Between Two Values

When you need an integer between two specific values, you incorporate both Math.random() and some arithmetic:

function getRandomInt(min: number, max: number): number {
  min = Math.ceil(min);
  max = Math.floor(max);
  return Math.floor(Math.random() * (max - min + 1)) + min;
}

const randomInt = getRandomInt(1, 10);
console.log(randomInt);

This might output an integer value between 1 and 10, such as 7.

Generating a Unique Identifier

Random numbers can be combined with other methods to create unique identifiers, for instance, a simple UUID generator snippet:

function generateUUID(): string {
    return 'xxxxyxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, (c) => {
        const r = Math.random() * 16 | 0, v = c == 'x' ? r : (r & 0x3 | 0x8);
        return v.toString(16);
    });
}

const uuid = generateUUID();
console.log(uuid);

This generates a string resembling a UUID, such as 110e8400-e29b-41d4-a716-446655440000.

Deep Dive

The primary method for generating random numbers in JavaScript and thus in TypeScript, Math.random(), relies on a pseudo-random number generator (PRNG). It’s important to note that while the results may seem random, they are generated by a deterministic algorithm based on an initial seed value. Therefore, numbers produced by Math.random() are not truly random and should not be used for cryptographic purposes.

For cryptographically secure random numbers, the Web Crypto API offers crypto.getRandomValues(), which is accessible in environments supporting the Web Crypto standard, including modern browsers and Node.js (via the crypto module). Here’s a quick example illustrating its use in TypeScript for generating a secure random number within a range:

function secureRandom(min: number, max: number): number {
    const array = new Uint32Array(1);
    window.crypto.getRandomValues(array);
    return min + (array[0] % (max - min + 1));
}

const secureRandNum = secureRandom(1, 100);
console.log(secureRandNum);

This method provides a stronger level of randomness and is more suited for security-sensitive applications. However, it’s also more resource-intensive and may not be necessary for more mundane tasks, like simple simulations or non-critical random value generation.

Rounding numbers