Why is eslint ignoring my strictNullChecks setting? - reactjs

Question

I am trying to port a large existing JavaScript codebase to TypeScript. I have installed typescript, #typescript-eslint/eslint-plugin and #typescript-eslint/parser as devDependencies and configured the project so that tsconfig.json is used.
My (minimal) tsconfig.json is:
{
"compilerOptions": {
"target": "es5",
"module": "esnext",
"alwaysStrict": true,
"strict": true,
"strictNullChecks": true
},
}
Running eslint on an existing .tsx file (correctly) shows some errors:
$ ./node_modules/.bin/eslint ./src/components/JustSomeComponent.tsx
/src/components/JustSomeComponent.tsx
57:75 error Unexpected empty arrow function 'myFunction' #typescript-eslint/no-empty-function
...
✖ 20 problems (8 errors, 12 warnings)
4 errors and 0 warnings potentially fixable with the `--fix` option.
However, I wanted to make sure that strictNullChecks setting was indeed enabled, so I created a new file and made a mistake on purpose:
import React from 'react';
export default class MyComponent extends React.Component {
render(): React.ReactNode {
const x: number = null; // I would expect an error here!
console.log(x);
return null;
}
}
But running the check on this file returns no errors:
$ ./node_modules/.bin/eslint ./src/components/MyComponent.tsx
$
Removing the return type for render() method results in an error, so the checks are performed - I am just not warned about invalid null assignements.
Any idea how I can enable strictNullChecks, or at least how to debug why it is disabled?

Answer 1

strictNullChecks is a TypeScript feature, not an ESLint feature.

Answer 2

As #jonrsharpe commented, strictNullChecks is a compiler setting and does not affect eslint.
The reason I wasn't getting any error was that eslint found errors in other files and prevented build from starting. Once I fixed those, build step indeed failed with an error as expected:
$ npm run build
> myapp#0.0.1 build
> react-scripts build
Creating an optimized production build...
Failed to compile.
/src/components/MyComponent.tsx
TypeScript error in /src/components/MyComponent.tsx(5,11):
Type 'null' is not assignable to type 'number'. TS2322
3 | export default class MyComponent extends React.Component {
4 | render(): React.ReactNode {
> 5 | const x: number = null;
| ^
6 | console.log(x);
7 | return null;
8 | }