no-floating-promises

Requires Promise-like statements to be handled appropriately.

A "floating" Promise is one that is created without any code set up to handle any errors it might throw.

Floating 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 it
• returning it
• Calling its .then() with two arguments
• Calling its .catch() with one argument

tip

no-floating-promises only detects unhandled Promise statements. See no-misused-promises for detecting code that provides Promises to logical locations such as if statements.

Rule Details

Examples of code for this rule:

❌ Incorrect

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

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

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

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

✅ Correct

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;
  // if true, checking for async iife will be skipped
  ignoreIIFE?: boolean;
};

const defaults = {
  ignoreVoid: true,
  ignoreIIFE: false,
};

ignoreVoid

This allows you to stop the rule reporting promises consumed with void operator. This can be a good way to explicitly mark a promise as intentionally not awaited.

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

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

void Promise.reject('value');

With this option set to true, and if you are using no-void, you should turn on the allowAsStatement option.

ignoreIIFE

This allows you to skip checking of async IIFEs (Immediately Invocated function Expressions).

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

await(async function () {
  await res(1);
})();

(async function () {
  await res(1);
})();

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

• no-misused-promises
• TSLint: 'no-floating-promises'

Attributes

• Configs:
  • ✅ Recommended
  • 🔒 Strict
• 🔧 Fixable
• 💭 Requires type information