A javascript promise that can tell you if it's been fulfilled.

promise-queryable.js

Promise.prototype.getQueryable = function () {
    if (this.isFulfilled) return this;

    let isPending = true;
    let isRejected = false;
    let isFulfilled = false;
    let value = undefined;
    let error = undefined;

    let result = this.then(v => {
        value = v;
        isFulfilled = true;
        isPending = false;
        return v;
    }, e => {
        error = e;
        isRejected = true;
        isPending = false;
        throw e;
    });

    result.isFulfilled = () => isFulfilled;
    result.isPending = () => isPending;
    result.isRejected = () => isRejected;
    result.value = () => value;
    result.error = () => error;

    return result;
}

/**** Example ******
const apiCall = fetch('/api').getQueryable();
if (apiCall.isPending()) {
  console.log('still waiting for request to finish');
} else if (apiCall.isFulfilled()) {
  console.log('response', apiCall.value());
} else {
  // Must have errorer
  console.log('error from fetch', apiCall.error());
}
*****************/