How Can I Seed Random Number Generators in JavaScript?

Seeding the Random Number Generator in JavaScript

The built-in Math.random() in JavaScript does not provide the ability to seed the random number generator, meaning that it cannot be initialized with a specific value to generate a predetermined sequence of random numbers.

While seeding is not possible with Math.random(), there are external libraries and implementations that offer custom functions for generating seedable pseudorandom numbers. Here are a few options:

Pseudorandom Number Generator (PRNG) Functions

Several compact and efficient PRNG functions can be implemented in JavaScript, providing high-quality random numbers that can be seeded with one or more 32-bit numbers.

Seed Initialization

It is crucial to initialize your PRNGs properly to avoid low-entropy seeds that can affect the randomness of the generated numbers. Here are two common methods:

• Hash Functions: Hash functions can generate seeds from short strings, allowing you to use a string as a seed. For instance, the cyrb128 hash function can produce a 128-bit hash value from a string.
• Dummy Data Padding: Alternatively, you can pad the seed with dummy data and advance the generator a few times to mix the initial state thoroughly.

PRNG Algorithms

Here's an example of the sfc32 (Simple Fast Counter) algorithm, which has a 128-bit state and produces random numbers in the range 0-1:

function sfc32(a, b, c, d) {
  return function() {
    a |= 0; b |= 0; c |= 0; d |= 0;
    let t = (a + b | 0) + d | 0;
    d = d + 1 | 0;
    a = b ^ b >>> 9;
    b = c + (c << 3) | 0;
    c = (c << 21 | c >>> 11);
    c = c + t | 0;
    return (t >>> 0) / 4294967296;
  }
}

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