in javascript you can't seed Math.random, if you want something you can seed you have to implement a PRNG yourself

i needed a function that returned a "random" value in [0, 1), like Math.random does, but seedable. importantly, it wasn't for anything even slightly cryptographic or whatever. i had absolutely no requirements for the quality of the output beyond "seems vaguely random to a person"

so here's the simplest, and probably worst (but good enough) PRNG function i found online:

let seed = WHATEVER_NUMBER;
function random() {
    const x = seed++/Math.PI;
    return x - Math.floor(x);
}