noMisusedPromises

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TypeScript and TSX

Summary

Rule available since: v2.1.0
Diagnostic Category: lint/nursery/noMisusedPromises
This rule has an unsafe fix.
The default severity of this rule is information.
This rule belongs to the following domains:
- project
Sources:
- Same as @typescript-eslint/no-misused-promises

Description

Disallow Promises to be used in places where they are almost certainly a mistake.

In most cases, if you assign a Promise somewhere a Promise is not allowed, the TypeScript compiler will be able to catch such a mistake. But there are a few places where TypeScript allows them — they’re not necessarily a mistake — even though they could be considered almost certainly to be one.

This rule disallows using Promises in such places.

Examples

Invalid

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const promise = Promise.resolve('value');
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if (promise) { /* This branch will always execute */ }

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const promise = Promise.resolve('value');
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const val = promise ? 123 : 456; // Always evaluates to `123`.

1
// The following filter has no effect:
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const promise = Promise.resolve('value');
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[1, 2, 3].filter(() => promise);

1
const promise = Promise.resolve('value');
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while (promise) { /* This is an endless loop */ }

1
// Using a `Promise` as an iterable expands to nothing:
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const getData = () => fetch('/');
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console.log({ foo: 42, ...getData() });

1
// These `fetch`-es are not `await`-ed in order:
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[1, 2, 3].forEach(async value => {
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    await fetch(`/${value}`);
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});

Valid

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const promise = Promise.resolve('value');
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if (await promise) { /* Do something */ }
3

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const val = (await promise) ? 123 : 456;
5

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while (await promise) { /* Do something */ }
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const getData = () => fetch('/');
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console.log({ foo: 42, ...(await getData()) });
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// for-of puts `await` in outer context:
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for (const value of [1, 2, 3]) {
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    await doSomething(value);
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}

How to configure

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{
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  "linter": {
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    "rules": {
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      "nursery": {
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        "noMisusedPromises": "error"
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      }
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    }
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  }
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}