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return-await

Enforce consistent awaiting of returned promises.

✅

Extending "plugin:@typescript-eslint/recommended-type-checked" in an ESLint configuration enables this rule.

🔧

Some problems reported by this rule are automatically fixable by the --fix ESLint command line option.

💡

Some problems reported by this rule are manually fixable by editor suggestions.

💭

This rule requires type information to run.

This rule builds on top of the eslint/no-return-await rule. It expands upon the base rule to add support for optionally requiring return await in certain cases.

The extended rule is named return-await instead of no-return-await because the extended rule can enforce the positive or the negative. Additionally, while the core rule is now deprecated, the extended rule is still useful in many contexts:

How to Use​

.eslintrc.cjs
module.exports = {
  "rules": {
    // Note: you must disable the base rule as it can report incorrect errors
    "no-return-await": "off",
    "@typescript-eslint/return-await": "error"
  }
};

Try this rule in the playground ↗

Options​

See eslint/no-return-await's options.

type Options =
  | 'in-try-catch'
  | 'always'
  | 'error-handling-correctness-only'
  | 'never';

const defaultOptions: Options = 'in-try-catch';

The options in this rule distinguish between "ordinary contexts" and "error-handling contexts". An error-handling context is anywhere where returning an unawaited promise would cause unexpected control flow regarding exceptions/rejections. See detailed examples in the sections for each option.

  • If you return a promise within a try block, it should be awaited in order to trigger subsequent catch or finally blocks as expected.
  • If you return a promise within a catch block, and there is a finally block, it should be awaited in order to trigger the finally block as expected.
  • If you return a promise between a using or await using declaration and the end of its scope, it should be awaited, since it behaves equivalently to code wrapped in a try block followed by a finally.

Ordinary contexts are anywhere else a promise may be returned. The choice of whether to await a returned promise in an ordinary context is mostly stylistic.

With these terms defined, the options may be summarized as follows:

OptionOrdinary Context
(stylistic preference 🎨)		Error-Handling Context
(catches bugs 🐛)		Should I use this option?
alwaysreturn await promise;return await promise;✅ Yes!
in-try-catchreturn promise;return await promise;✅ Yes!
error-handling-correctness-onlydon't care 🤷return await promise;🟡 Okay to use, but the above options would be preferable.
neverreturn promise;return promise;
(⚠️ This behavior may be harmful ⚠️)		❌ No. This option is deprecated.

in-try-catch​

In error-handling contexts, the rule enforces that returned promises must be awaited. In ordinary contexts, the rule enforces that returned promises must not be awaited.

This is a good option if you prefer the shorter return promise form for stylistic reasons, wherever it's safe to use.

Examples of code with in-try-catch:

async function invalidInTryCatch1() {
  try {
    return Promise.reject('try');
  } catch (e) {
    // Doesn't execute due to missing await.
  }
}

async function invalidInTryCatch2() {
  try {
    throw new Error('error');
  } catch (e) {
    // Unnecessary await; rejections here don't impact control flow.
    return await Promise.reject('catch');
  }
}

// Prints 'starting async work', 'cleanup', 'async work done'.
async function invalidInTryCatch3() {
  async function doAsyncWork(): Promise<void> {
    console.log('starting async work');
    await new Promise(resolve => setTimeout(resolve, 1000));
    console.log('async work done');
  }

  try {
    throw new Error('error');
  } catch (e) {
    // Missing await.
    return doAsyncWork();
  } finally {
    console.log('cleanup');
  }
}

async function invalidInTryCatch4() {
  try {
    throw new Error('error');
  } catch (e) {
    throw new Error('error2');
  } finally {
    // Unnecessary await; rejections here don't impact control flow.
    return await Promise.reject('finally');
  }
}

async function invalidInTryCatch5() {
  return await Promise.resolve('try');
}

async function invalidInTryCatch6() {
  return await 'value';
}

async function invalidInTryCatch7() {
  using x = createDisposable();
  return Promise.reject('using in scope');
}
Open in Playground

always​

Requires that all returned promises be awaited.

This is a good option if you like the consistency of simply always awaiting promises, or prefer not having to consider the distinction between error-handling contexts and ordinary contexts.

Examples of code with always:

async function invalidAlways1() {
  try {
    return Promise.resolve('try');
  } catch (e) {}
}

async function invalidAlways2() {
  return Promise.resolve('try');
}

async function invalidAlways3() {
  return await 'value';
}
Open in Playground

error-handling-correctness-only​

In error-handling contexts, the rule enforces that returned promises must be awaited. In ordinary contexts, the rule does not enforce any particular behavior around whether returned promises are awaited.

This is a good option if you only want to benefit from rule's ability to catch control flow bugs in error-handling contexts, but don't want to enforce a particular style otherwise.

info

We recommend you configure either in-try-catch or always instead of this option. While the choice of whether to await promises outside of error-handling contexts is mostly stylistic, it's generally best to be consistent.

Examples of additional correct code with error-handling-correctness-only:

async function asyncFunction(): Promise<void> {
  if (Math.random() < 0.5) {
    return await Promise.resolve();
  } else {
    return Promise.resolve();
  }
}
Open in Playground

never​

Disallows awaiting any returned promises.

warning

This option is deprecated and will be removed in a future major version of typescript-eslint.

The never option introduces undesirable behavior in error-handling contexts. If you prefer to minimize returning awaited promises, consider instead using in-try-catch instead, which also generally bans returning awaited promises, but only where it is safe not to await a promise.

See more details at typescript-eslint#9433.

Examples of code with never:

async function invalidNever1() {
  try {
    return await Promise.resolve('try');
  } catch (e) {}
}

async function invalidNever2() {
  return await Promise.resolve('try');
}

async function invalidNever3() {
  return await 'value';
}
Open in Playground

When Not To Use It​

Type checked lint rules are more powerful than traditional lint rules, but also require configuring type checked linting.

See Troubleshooting > Linting with Type Information > Performance if you experience performance degredations after enabling type checked rules.

Resources​

Taken with ❤️ from ESLint core.