catch-or-return.md

Enforce the use of catch() on un-returned promises (promise/catch-or-return)

💼 This rule is enabled in the following configs: ✅ flat/recommended, ✅ recommended.

Ensure that each time a then() is applied to a promise, a catch() is applied as well. Exceptions are made if you are returning that promise.

Valid

myPromise.then(doSomething).catch(errors)
myPromise.then(doSomething).then(doSomethingElse).catch(errors)
function doSomethingElse() {
  return myPromise.then(doSomething)
}

Invalid

myPromise.then(doSomething)
myPromise.then(doSomething, catchErrors) // catch() may be a little better
function doSomethingElse() {
  return myPromise.then(doSomething)
}

Options

allowThen

The second argument to then() can also be used to handle a promise rejection, but it won't catch any errors from the first argument callback. Because of this, this rule reports usage of then() with two arguments without catch() by default.

However, you can use { allowThen: true } to allow using then() with two arguments instead of catch() to handle promise rejections.

Examples of incorrect code for the default { allowThen: false } option:

myPromise.then(doSomething, handleErrors)
myPromise.then(null, handleErrors)

Examples of correct code for the { allowThen: true } option:

myPromise.then(doSomething, handleErrors)
myPromise.then(null, handleErrors)
myPromise.then(doSomething).catch(handleErrors)

allowThenStrict

allowThenStrict is similar to allowThen but it only permits then when the fulfillment handler is null. This option ensures that the final rejected handler works like a catch and can handle any uncaught errors from the final then.

Examples of incorrect code for the default { allowThenStrict: false } option:

myPromise.then(doSomething, handleErrors)
myPromise.then(null, handleErrors)

Examples of correct code for the { allowThenStrict: true } option:

myPromise.then(null, handleErrors)
myPromise.then(doSomething).catch(handleErrors)

Examples of incorrect code for the { allowThenStrict: true } option:

myPromise.then(doSomething, handleErrors)

allowFinally

You can pass an { allowFinally: true } as an option to this rule to allow for .finally(fn) to be used after catch() at the end of the promise chain. This is different from adding 'finally' as a terminationMethod because it will still require the Promise chain to be "caught" beforehand.

terminationMethod

You can pass a { terminationMethod: 'done' } as an option to this rule to require done() instead of catch() at the end of the promise chain. This is useful for many non-standard Promise implementations.

You can also pass an array of methods such as { terminationMethod: ['catch', 'asCallback', 'finally'] }.

This will allow any of

Promise.resolve(1)
  .then(() => {
    throw new Error('oops')
  })
  .catch(logerror)
Promise.resolve(1)
  .then(() => {
    throw new Error('oops')
  })
  .asCallback(cb)
Promise.resolve(1)
  .then(() => {
    throw new Error('oops')
  })
  .finally(cleanUp)