Feature: require await (particularly return await) whereever promises are used

[coolaj86]

There's an entire class of error that can be categorically eliminated by always using await whenever there is a promise.

Consider this simple refactor:

async function doStuff() {
  return theOnlyFunctionIThoughtIWouldEverNeed();
}

async function doStuff() {
  let x = theOnlyFunctionIThoughtIWouldEverNeed();
  let y = doMoreThings(x); // error, expected 'x' to be a value, not a promise
  return y;
}

or this one, following the "return something, or return nothing" philosophy:

async function doStuff() {
  theOnlyFunctionIThoughtIWouldEverNeed();
}

which should instead be

async function doStuff() {
  await theOnlyFunctionIThoughtIWouldEverNeed();
}

Also, await lends clarity to the reader when it's non-obvious that the function being called is a promise / async function.

Hence the original should be:

async function doStuff() {
  return await theOnlyFunctionIThoughtIWouldEverNeed();
}

I would put this in the same category as curly: true in terms of its usefulness and the kinds of problems that it solves.

[kaizhu256]

do you mean to change the title to:

-Feature: require await (particularly return await) whereever promises are used
+Feature: require await (particularly return await) for async functions

detecting whether objects are thenable is probably out-of-scope for linters.

[jugglinmike]

Thanks for taking the time to write a report! It's always nice to hear from folks looking to make programming safer.

This kind of behavior may not be possible to implement for JavaScript code, though, since JavaScript is dynamically typed. Expressions like identifier references and function invocations can evaluate to any value, so it's tough to enforce rules like this through static analysis of the source code. This may be what @kaizhu256 had in mind, as well.

There's also the non-syntactic ways to consume Promises to consider, e.g. Promise.all.

For what it's worth, this is definitely feasible with a typed language like TypeScript.