typescript/no-misused-promises Pedantic

What it does

This rule forbids providing Promises to logical locations such as if statements in places where the TypeScript compiler allows them but they are not handled properly. These situations can often arise due to a missing await keyword or just a misunderstanding of the way async functions are handled/awaited.

Why is this bad?

Misused promises can cause crashes or other unexpected behavior, unless there are possibly some global unhandled promise handlers registered.

Examples

Examples of incorrect code for this rule:

// Promises in conditionals:
const promise = Promise.resolve("value");
if (promise) {
  // Do something
}

// Promises where `void` return was expected:
[1, 2, 3].forEach(async (value) => {
  await fetch(`/${value}`);
});

// Spreading Promises:
const getData = () => fetch("/");
console.log({ foo: 42, ...getData() });

Examples of correct code for this rule:

// Awaiting the Promise to get its value in a conditional:
const promise = Promise.resolve("value");
if (await promise) {
  // Do something
}

// Using a `for-of` with `await` inside (instead of `forEach`):
for (const value of [1, 2, 3]) {
  await fetch(`/${value}`);
}

// Spreading data returned from Promise, instead of the Promise itself:
const getData = () => fetch("/");
console.log({ foo: 42, ...(await getData()) });

Configuration

This rule accepts a configuration object with the following properties:

checksConditionals

type: boolean

default: true

Whether to check if Promises are used in conditionals. When true, disallows using Promises in conditions where a boolean is expected.

checksSpreads

type: boolean

default: true

Whether to check if Promises are used in spread syntax. When true, disallows spreading Promise values.

checksVoidReturn

type: object | boolean

checksVoidReturn.arguments

type: boolean

default: true

Whether to check Promise-returning functions passed as arguments to void-returning functions.

checksVoidReturn.attributes

type: boolean

default: true

Whether to check Promise-returning functions in JSX attributes expecting void.

checksVoidReturn.inheritedMethods

type: boolean

default: true

Whether to check Promise-returning methods that override void-returning inherited methods.

checksVoidReturn.properties

type: boolean

default: true

Whether to check Promise-returning functions assigned to object properties expecting void.

checksVoidReturn.returns

type: boolean

default: true

Whether to check Promise values returned from void-returning functions.

checksVoidReturn.variables

type: boolean

default: true

Whether to check Promise-returning functions assigned to variables typed as void-returning.

How to use

To enable this rule using the config file or in the CLI, you can use:

Config (.oxlintrc.json)

{
  "rules": {
    "typescript/no-misused-promises": "error"
  }
}

CLI

oxlint --type-aware --deny typescript/no-misused-promises

References

• Rule Source
• Rule Source (tsgolint)