Dedupe racing promises by arguments

dedupe.ts

export class PromiseCacher<T extends (...args: any[]) => Promise<any>> {
    private cache: Map<string, Promise<any>> = new Map();
    private fn: T;

    constructor(fn: T) {
        this.fn = fn;
    }

    execute(...args: Parameters<T>): ReturnType<T> {
        const key = JSON.stringify(args);

        if (this.cache.has(key)) {
            return this.cache.get(key) as ReturnType<T>;
        }

        const promise = this.fn(...args);
        this.cache.set(key, promise);

        promise.finally(() => {
            this.cache.delete(key);
        });

        return promise as ReturnType<T>;
    }
}
  
// example

const fetchPromiseCache = new PromiseCacher(async function  fetcher(src: string) {
    return await fetch(src);
});

const [a, b] = await Promise.all([fetchPromiseCache.execute('/hello'), fetchPromiseCache.execute('/hello')]);
console.log(a === b); // true

const [a2, b2] = await Promise.all([fetch('/hello'), fetch('/hello')]);
console.log(a2 === b2); // false