Intellij Idea warning - “Promise returned is ignored” with aysnc/await

Question

I\'m using Express.js in my code with Node.js v7.3. In this I\'ve created a User Router which forwards the requests to my User Controlle

Answer 1

another way to get rid of the warning is defining an empty then():

userController.login(req, res); // <- Get the warning here

userController.login(req, res).then(); // <- No warning

Answer 2

router.post('/login', function (req, res, next) {
    void userController.login(req, res); // I get the warning here
});

You should use "void" operator.

Answer 3

The userController.login() function returns a promise, but you're not doing anything with the result from the promise by utilizing its then() function.

For example:

userController.login(req, res).then(() => {
    // Do something after login is successful.
});

or in the ES2017 syntax:

await userController.login(req, res);

If you don't actually want to do anything there, I guess you can just ignore the warning. The warning is mostly there because not using the then() function on a promise is usually a code smell.

Answer 4

if you are really manic as me and the then() is not required but you need the warning to go away, a possible solution is:

functionWithAsync.error(console.error);

Answer 5

The thing is I'm not even returning anything from the login() method.

A function declared "async" returns a Promise by definition. See for example https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/async_function

However the IDEA warning is only an inspection. You can press "alt-enter, right" on the warning and change the inspection level to make the warning go away. The inspection is in the "JavaScript -> Probable bugs" category and is named "Result of method call returning a promise is ignored".

Answer 6

I'm using try{} catch(e){} in NodeJs and found that simply adding Error() to the end of the function fixed the warning.

Full code:-

someArray.forEach(async (arrayValue) => {
    try {
        const prodData = await myAsyncFunc(arrayValue);
    } catch(e) {
        console.error(`Error: ${e}`);
    }
}, Error());