Detect missing await in JavaScript methods in VSCode

Question

I'm searching for some eslint option, or some other way to detect missing the 'await' keyword before calling async methods inside a class. Consider the following code:

const externalService = require('./external.service');

class TestClass {

constructor() { }

async method1() {
    if (!await externalService.someMethod()) {
        await this.method2();
    }
}

async method2() {
    await externalService.someOtherMethod();
}

module.exports = TestClass;

There will be no warning if I will convert method1 to:

async method1() {
    if (!await externalService.someMethod()) {
        this.method2();
    }
}

I tried to do on the '.eslintrc' file:

"require-await": 1,
"no-return-await": 1,

But with no luck. Anyone have an idea if it is even possible? Thanks a lot!

Answer 1

typescript-eslint has a rule for this: no-floating-promises

This rule forbids usage of Promise-like values in statements without handling their errors appropriately ... Valid ways of handling a Promise-valued statement include awaiting, returning, and either calling .then() with two arguments or .catch() with one argument.

As you probably figured out from the name, typescript-eslint is designed to add TypeScript support to eslint, but you can use it with JavaScript as well. I guess it's your call to decide whether it's overkill for this one rule, but here are the steps:

1. Generate a tsconfig.json file

   npx tsc --init
   

2. Install dependencies

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

3. Modify your .eslintrc file

   Based on my testing it looks like you'll need these entries at a minimum:

   {
     "parser": "@typescript-eslint/parser",
     "parserOptions": { "project": "./tsconfig.json" },
     "plugins": ["@typescript-eslint"],
     "rules": {
       "@typescript-eslint/no-floating-promises": ["error"]
     }
   }
   

If there are places where you want to call an async function without using await, you can either:

• Use the void operator as mentioned in the documentation for the rule, e.g.

  void someAsyncFunction();
  

• Or just change error to warn in the .eslintrc configuration above

The documentation for setting up typescript-eslint is here for more info: https://typescript-eslint.io/docs/linting/linting

Next time you run eslint you should see the rule applied:

$ npm run lint
...
./services/jobService.js
  11:5  warning  Promises must be awaited, end with a call to .catch, end with a call to .then with a rejection handler or be explicitly marked as ignored with the `void` operator  @typescript-eslint/no-floating-promises

Since you mentioned VS Code specifically, this also integrates great with the ESLint plugin: