Is there a way to tell if an ES6 promise is fulfilled/rejected/resolved? [duplicate]

Question

I'm used to Dojo promises, where I can just do the following:

promise.isFulfilled(); promise.isResolved(); promise.isRejected(); 

Is there a way to determine if an ES6 promise is fulfilled, resolved, or rejected? If not, is there a way to fill in that functionality using Object.defineProperty(Promise.prototype, ...)?

Answer 1

They are not part of the specification nor is there a standard way of accessing them that you could use to get the internal state of the promise to construct a polyfill. However, you can convert any standard promise into one that has these values by creating a wrapper,

function MakeQueryablePromise(promise) {     // Don't create a wrapper for promises that can already be queried.     if (promise.isResolved) return promise;          var isResolved = false;     var isRejected = false;      // Observe the promise, saving the fulfillment in a closure scope.     var result = promise.then(        function(v) { isResolved = true; return v; },         function(e) { isRejected = true; throw e; });     result.isFulfilled = function() { return isResolved || isRejected; };     result.isResolved = function() { return isResolved; }     result.isRejected = function() { return isRejected; }     return result; } 

This doesn't affect all promises, as modifying the prototype would, but it does allow you to convert a promise into a promise that exposes it state.