Bug: "use strict" should not trigger strict mode in ES3

Environment

ESLint version: 8.5.0

What parser are you using?

Default (Espree)

What did you do?

Configuration

{
    "parserOptions": {
        "ecmaVersion": 3
    }
}

"use strict";
alert(00);

What did you expect to happen?

Merry Christmas!

No error is expected here. ES3 has no strict mode, the "use strict" directive should be ignored, and legacy octal literals like 00 should be always allowed. In fact, the code above works in IE 6…

What actually happened?

Parser error: invalid number (demo link)

Participation

• I am willing to submit a pull request for this issue.

Additional comments

No response

[nzakas]

Because this is a parsing error and not a linting error, that means it’s coming from Acorn and not ESLint. I’d suggest opening up an issue on Acorn to see what their response is. They usually have a good reason for seemingly incorrect behavior like this that may not be obvious, and if not, they’ll know the best approach to address it.

[ljharb]

I agree there’s some philosophical interest in being able to lint ES3 code and ignore the strict pragma, but as I stated above, I don’t think there’s any use in that being by default. It could certainly be done via an option, if the eslint folks wanted to maintain that complexity.