TypeScript - own random number generator (custom implementation)

In this article, we're going to have a look at how to write own random numbers generator that is based on LCG (Linear congruential generator) algorithm in TypeScript.

1. Introduction

In TypeScript, we can implement a custom random number generator by using LCG (Linear congruential generator) algorithm. LCG is one of the oldest and best-known pseudorandom number generator algorithm. We can adjust this implementation to work on int or long.

The linear congruential generator is defined by the recurrence formula:

Where:

• Xn+1 - new seed,
• a - multiplier,
• Xn - current seed (comes from previous calculations),
• c - incrementer,
• m - modulus (max integer value).

2. Implementation

Note: every time randomInt() method is called, it is necessary to update seed value.

class CustomRandom {
    private A: number = 1103515245; // multiplier
    private C: number = 12345;      // incrementer
    private M: number = 2147483647; // modulus == max integer value

    public constructor(private seed: number = Date.now()) { /* Nothing here ... */ }

    public nextInt = (): number => {
        this.seed = (this.seed * this.A + this.C) % this.M;
        return this.seed;
    };

    public nextDouble = (): number => {
        const value = this.nextInt();
        return value / this.M;
    };
}


// Usage example 1:

const random1 = new CustomRandom(3819201); // 3819201 is example initial seed

console.log(random1.nextInt()); // 348328093
console.log(random1.nextInt()); // 121065958
console.log(random1.nextInt()); // 790325445


// Usage example 2 (values should be different always):

const random2 = new CustomRandom();

console.log(random2.nextInt()); // 922892575
console.log(random2.nextInt()); // 1117277734
console.log(random2.nextInt()); // 2084933141

console.log(random2.nextDouble()); // 0.6316955399847103
console.log(random2.nextDouble()); // 0.5716405932659472
console.log(random2.nextDouble()); // 0.3298228519641901