Stricter `no-undef` default

Tell us about your environment

• ESLint Version: 5.0.0-alpha
• Node Version: 10.0.0-pre
• npm Version: 5.6

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

Default

Please show your full configuration:

no-undef: error

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

if (typeof undef === 'string') {
  throw new Error('foobar')
}

What did you expect to happen?

An error should be reported. This is possible by using the typeof option. I personally feel this option should be activated by default as I do not see a reason why it such statements are not validated by default.

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

No error is reported by default.

[platinumazure]

I’m mildly opposed to making a breaking change here because of the fact that this is behaving like the language spec, and we do have the option available. I’m not convinced that there is much benefit to making the breaking change.

[btmills]

Thanks all for the discussion on this. Since we have split opinions on this issue and there hasn’t been any further discussion in almost 3 years, I’ll close this instead of bumping it again to another release.