no-undefined doesn't allow undefined as an object property

Tell us about your environment

• ESLint Version: v3.14.0
• Node Version: v6.9.4
• npm Version: 3.10.10

What parser (default, Babel-ESLint, etc.) are you using? default

Please show your full configuration:

{
  "parserOptions": {
    "ecmaVersion": 6
  },
  "env": {
    "browser": true
  },
  "globals": {
    "jQuery": false
  },
  "rules": {
    "quote-props": ["error", "consistent-as-needed"],
    "no-undefined": "error"
  }
}

What did you do? Please include the actual source code causing the issue.

'use strict';

var foo = {
  undefined: 'bar',
};

What did you expect to happen? undefined should be permitted as an unquoted object property.

What actually happened? Please include the actual, raw output from ESLint. no-undefined produces an error. Quoting undefined (which would otherwise be a workaround) produces an error from quote-props.

Given that undefined is a permissable object property name, I believe no-undefined should be modified to permit this behaviour.

[ljharb]

They might only be valid in strict mode, with an ecmaVersion > 5 or 6 - but I think there’s other rules that can handle that.

var { undefined: bar } = foo; should be valid because it’s extracting a property named “undefined” and putting it into a variable named “bar” - but I don’t think var { bar: undefined } = foo; should be valid since it’s creating a variable named “undefined” from foo.bar.

[platinumazure]

Okay. I assume that assigning to undefined should probably be invalid in each case, then, since it’s still trying to use undefined as an identifier rather than it coming up as an object key. I’ll write a PR with that assumption, let me know either here or in the PR if that’s wrong.