no-floating-promises.md

Requires Promise-like values to be handled appropriately (no-floating-promises)

This rule forbids usage of Promise-like values in statements without handling their errors appropriately. Unhandled promises can cause several issues, such as improperly sequenced operations, ignored Promise rejections and more. Valid ways of handling a Promise-valued statement include awaiting, returning, and either calling .then() with two arguments or .catch() with one argument.

Rule Details

Examples of incorrect code for this rule:

const promise = new Promise((resolve, reject) => resolve('value'));
promise;

async function returnsPromise() {
  return 'value';
}
returnsPromise().then(() => {});

Promise.reject('value').catch();

Promise.reject('value').finally();

Examples of correct code for this rule:

const promise = new Promise((resolve, reject) => resolve('value'));
await promise;

async function returnsPromise() {
  return 'value';
}
returnsPromise().then(
  () => {},
  () => {},
);

Promise.reject('value').catch(() => {});

Promise.reject('value').finally(() => {});

Options

The rule accepts an options object with the following properties:

type Options = {
  // if true, checking void expressions will be skipped
  ignoreVoid?: boolean;
};

const defaults = {
  ignoreVoid: false,
};

ignoreVoid

This allows to easily suppress false-positives with void operator.

Examples of correct code for this rule with { ignoreVoid: true }:

async function returnsPromise() {
  return 'value';
}
void returnsPromise();

void Promise.reject('value');

When Not To Use It

If you do not use Promise-like values in your codebase or want to allow them to remain unhandled.

Related to

• TSLint: 'no-floating-promises'