How to Create a Seedable Random Number Generator in JavaScript?

Seedable JavaScript Random Number Generator

The JavaScript Math.random() function generates random values between 0 and 1 based on the current time, similar to Java's random number generator. However, it lacks the ability to specify a seed value to control the sequence of generated numbers.

Creating a Custom Random Number Generator with Seed Support

To create a random number generator with seed support, consider the following options:

Implementing a Linear Congruential Generator (LCG)

LCGs are relatively simple to implement and provide decent randomness qualities. You can utilize the following constants:

m = 0x80000000; // 2**31
a = 1103515245;
c = 12345;

Here's an example implementation in JavaScript:

<code class="javascript">function RNG(seed) {
  this.m = 0x80000000;
  this.a = 1103515245;
  this.c = 12345;

  this.state = seed ? seed : Math.floor(Math.random() * (this.m - 1));
}
RNG.prototype.nextInt = function() {
  this.state = (this.a * this.state + this.c) % this.m;
  return this.state;
}</code>

You can extend this RNG class to provide additional methods like nextFloat, nextRange, and choice based on the LCG core.

Utilizing Libraries for Short Seedable RNGs

Libraries such as [js-random](https://www.npmjs.com/package/js-random) provide short, seedable RNGs with options for different algorithms.

Example Implementation

Here's a simple example using an LCG-based RNG:

<code class="javascript">var rng = new RNG(20);
for (var i = 0; i < 10; i++) {
  console.log(rng.nextRange(10, 50));
}</code>

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