finally() not passing result #18

epernice · 2020-05-06T20:34:35Z

SynchronousPromise's finally() is not returning the resolved value (tried on 2.0.10). Here's a RunKit that compares the behavior against ES6 promises.
https://runkit.com/embed/cu88waw08blm

var SynchronousPromise = require("synchronous-promise").SynchronousPromise;

let result = null;

result = await Promise.resolve("foo");
console.log("es6 promise after resolve: " + result); // foo

result = await SynchronousPromise.resolve("foo");
console.log("sync promise after resolve: " + result); // foo

result = await Promise.resolve("foo").finally();
console.log("es6 promise after finally: " + result); // foo

result = await SynchronousPromise.resolve("foo").finally();
console.log("sync promise after finally: " + result); // undefined

The text was updated successfully, but these errors were encountered:

epernice · 2020-05-06T20:49:17Z

Here's how I'm working around it. Not sure whether there will be problems associated with this hack.

SynchronousPromise.prototype.finally = function(callback) {
    var ran = false;
    function runFinally() {
        if (!ran) {
            ran = true;
            return callback();
        }
    }
    return this
        .then(result => {
            runFinally();
            return result;
        })
        .catch(result => {
            runFinally();
            return result;
        });
};

Thanks, by the way, for this library! It's going to save me a LOT of work as I move a large codebase off of angular 1.x promises (with $httpBackend flushing to make tests synchronous) over to ES6 promises. I really wasn't looking forward to modifying thousands of tests to use async/await.

fluffynuts · 2020-05-08T07:50:33Z

@epernice resolved & published. Thanks for reporting, especially in so much detail (:

epernice · 2020-05-11T19:32:44Z

Thanks for the quick turnaround!

The change does pass in my original Runkit, but still failed against my codebase. It looks like there is still an additional difference that crops up when a function is passed into the finally:

var SynchronousPromise = require("synchronous-promise").SynchronousPromise;


8000
let result = null;

result = await Promise.resolve("foo");
console.log("es6 promise after resolve: " + result); // foo

result = await SynchronousPromise.resolve("foo");
console.log("sync promise after resolve: " + result); // foo

result = await Promise.resolve("foo").finally(() => {});
console.log("es6 promise after finally: " + result); // foo

result = await SynchronousPromise.resolve("foo").finally(() => {});
console.log("sync promise after finally: " + result); // undefined

fluffynuts · 2020-05-12T20:10:51Z

Ok, please check out 2.0.12 -- I added the test above (empty finally method) and then found that there were a couple of subtle differences between how native Promises in Firefox behaved than how SynchronousPromise behaved, with respect to finally handling. Some of the behaviors don't seem logical to me -- like discarding the result from finally except if it throws, but that's what native FF promises do, so 🤷 I've implemented the same.

fluffynuts · 2020-05-12T20:11:19Z

should be fixed in 0042d62

fluffynuts · 2020-05-12T20:15:46Z

btw, thanks for reporting -- as noted in the readme, I rely on user feedback to keep this library valuable (:

epernice · 2020-08-04T17:33:19Z

Sorry for not circling back to try this out sooner, but this solved it for me - thanks!

fluffynuts closed this as completed in 8504c61 May 8, 2020

fluffynuts reopened this May 12, 2020

fluffynuts closed this as completed May 12, 2020

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finally() not passing result #18

finally() not passing result #18

finally() not passing result #18

finally() not passing result #18

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