Wrapper for promise to resolve/reject externally and get indication whether the promise was fulfilled

deferred.ts

export class Deferred<T = void> {
    public resolve!: (value?: T | PromiseLike<T>) => void;
    public reject!: (reason?: any) => void;
    public readonly promise: Promise<T>;
    private isFulfilled = false;

    constructor() {
        this.promise = new Promise(
            (resolve, reject) => {
                this.resolve = resolve;
                this.reject = reject;
            })
            .finally(() => {
                this.isFulfilled = true;
            }) as Promise<T>;
    }

    get fulfilled() { return this.isFulfilled; }
}