Eslint does not recognize private field declaration using nodejs 12

2021 Update: You do not need babel for this anymore!

You can simply update eslint to v8.0.0 and above.

See eslint release notes: https://eslint.org/blog/2021/10/eslint-v8.0.0-released#highlights

Make sure this is in your .eslintrc file or similar:

{
    "parserOptions": {
        "ecmaVersion": 13
    }
}

You can also just use latest instead of specifically version 13.