always-catch.md

Pattern: Unreturned promise

Issue: -

Description

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.

Example of correct code:

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

Example of incorrect code:

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

Options

allowThen

You can pass an { allowThen: true } as an option to this rule to allow for .then(null, fn) to be used instead of catch() at the end of the promise chain.

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)

Further Reading

• eslint-plugin-promise - catch-or-return