eslint-plugin-async-promise

A typescript-eslint plugin to catch Promise related errors

• Installation
• Usage
• Rules
  • Rules/async-no-await
  • Rules/unnecessary-async

Installation

First, install the required packages for ESLint, TypeScript, TypeScript ESLint and the TypeScript ESLint Parser

npm install @typescript-eslint/parser @typescript-eslint/eslint-plugin eslint typescript --save-dev

Next, install eslint-plugin-async-promise:

$ npm install eslint-plugin-async-promise --save-dev

Note: If you installed ESLint globally (using the -g flag) then you must also install eslint-plugin-async-promise globally.

Usage

Add async-promise to the plugins section of your .eslintrc.json configuration file. You can omit the eslint-plugin- prefix:

{
  "plugins": ["async-promise"]
}

Then configure the rules you want to use under the rules section.

{
  "rules": {
    "async-promise/async-no-await": "error",
    "async-promise/unnecessary-async": "warn"
  }
}

Rules

async-no-await

Disallow concurrent async function calls inside an async function.

While we do not always need to await Promise (such as firing side-effects that do not block other calls), it is often a programmer error to forget adding await for these async callsinside an async function.

Examples

❌ Incorrect

function a() {
  return Promise.resolve();
}
async function b() {
  a(); // a() should have been awaited
  return Promise.resolve();
}

function a() {
  return Promise.resolve();
}
async function b() {
  a(); // a() should have been awaited since the return type is still Promise implicitly
  return "Not returning a Promise";
}

✅ Correct

function a() {
  return Promise.resolve();
}
async function b() {
  await a(); // Even if b() is not awaited, a() will always run before the return
  return Promise.resolve();
}

function a() {
    return Promise.resolve();
};
function b() {
    a(); // This is ok because the function is not marked as async, this can just be a side-effect
    return Promise.resolve();
};,

function a() {
  return Promise.resolve();
}
async function b() {
  const result = await Promise.all([a()]); // Skip checks async calls in Promise.all, if it's awaited
  return Promise.resolve();
}

unnecessary-async

Enforce that async keyword is only added when:

1. The function explicitly returns Promise
2. There is at least 1 await statement in the function

Examples

❌ Incorrect

function a() {
  return Promise.resolve();
}
async function b() {
  a();
}

async function b() {
  return "Not returning a Promise explicitly";
}

✅ Correct

async function b() {
  return Promise.resolve();
}

function a() {
    return Promise.resolve();
};
async function b() {
  await a();
};,

function a() {
    return Promise.resolve();
};
async function b() {
  return a();
};,

const a = {
  b: () => Promise.resolve(),
};
async function c() {
  // Example: MemberExpression : a.b()
  const result = await a.b();
  return result;
}