How to wait for a promise to be resolved?

Question

I'm dealing with a NodeJs framework that requires a certain function to be synchronous, but I need to retrieve a value that can only be accessed asynchronously. In a perfect world, I would be able to return a promise, but I can't.

As a quick-and-dirty solution, I created the following method:

exports.synchronizePromise = function(promise) {     var value;     promise.then(function(promiseValue) {         value = promiseValue;     });     while (!value) {} // Wait for promise to resolve     console.log("DONE: " + value); // Never reached     return value; }; 

But I get an error. Is there any way to accomplish what I need?

Answer 1

Given that node is by default only single threaded there isn't really an easy way to solve this. There is one though. Bases on generators/fibers you can add a sort of concurrent execution to node. There is a waitfor implementation based on that.

Answer 2

In Q if you have a resolved promise you can just take the value with inspect

exports.synchronizePromise = function(promise) {   var i = promise.inspect();     if (i.state === "rejected") {       throw i.reason;     } else if (i.state === "fulfilled") {       return i.value;     } else {       throw new Error("attempt to synchronize pending promise")     } }; 

However if the promise is pending, it is truly asynchronous and your question doesn't then make sense and the function will throw an error.