no-undef fails with node.js global object

Tell us about your environment

• ESLint Version: 5.12.1
• Node Version: 10.15.1
• npm Version: 6.4.1

What parser (default, Babel-ESLint, etc.) are you using? default Please show your full configuration:

Configuration

{
  "env": {
    "node": true
  },
  "extends": "eslint:recommended",
  "parserOptions": {
    "ecmaVersion": 2018
  }
}

What did you do? Please include the actual source code causing the issue, as well as the command that you used to run ESLint.

global.my_value = 5;

if (my_value < 3) {
  // ...
}

eslint . --ext .js

What did you expect to happen? No error would occur as the nodejs environment is set.

What actually happened? Please include the actual, raw output from ESLint.

/path/to/my/index.js
   3:5  error  'my_value' is not defined      no-undef

Are you willing to submit a pull request to fix this bug? No, I lack the experience with eslint internal code to reliably do so.

[not-an-aardvark]

Personally I don’t think this change would be worth the complexity, because:

• ESLint currently isn’t aware that global represents the global object in Node. The node env just enables some specific globals such as module, global, and exports (and also some unrelated parser options), but there isn’t any concept of “assignments to this value will create a property on the global object”.
• This won’t create a global if someone has reassigned global.global to something other than the global object.
• Determining whether a particular global is present at any given point is undecidable, since a property could also be conditionally deleted from the global object (or deleted in another file). On the other hand, determining whether a non-global variable is in scope is statically decidable for strict mode code.

[fregante]

TypeScript now also detects variables added on globalThis

https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-4.html#type-checking-for-globalthis