Update: add allow underscores options to camelcase rule.

[tinymins]

What is the purpose of this pull request? (put an "X" next to item)

[ ] Documentation update
[ ] Bug fix (template)
[ ] New rule (template)
[X] Changes an existing rule (template)
[ ] Add autofixing to a rule
[ ] Add a CLI option
[ ] Add something to the core
[ ] Other, please explain:

What changes did you make? (Give an overview)

Add options to control whether leading and trailing underscores are allowed in id naming.

Is there anything you'd like reviewers to focus on?

The default value. This option should be enabled because it was enabled in previous version.

[jsf-clabot]

All committers have signed the CLA.

[platinumazure]

I'm not sure this is necessary because you could use id-match for this sort of scenario as well.

[tinymins]

@platinumazure I've tried id-match. There're too much problems to use that, even Math.floor will be reported when use id-match.

[tinymins]

@platinumazure Here's the screenshot. Use id-match in current version cannot limit lower-camelcase in property. Rule id-match also need to be updated to satisfy this situation.

[platinumazure]

The reason I recommended id-match here is because the entire point of the camelcase rule is to forbid underscores. Maybe we could consider an enhancement for your specific use case, but id-match was created to allow users to specify their own identifier rules. (That said, the fact that you might need different rules for variables versus properties is probably something that id-match is not currently designed for. Not saying we can't enhance it, but rather that I hadn't been aware of your requirement before I had recommended that rule.)

Let's see what the rest of the team thinks.

[tinymins]

@platinumazure What you said is also what I want. Actually camelcase allows leading underscores now, but in my project we want to disallow any underscores. Shall we remove the leading and trailing underscores ignore code in rule camelcase?

[tinymins]

@platinumazure Here is the code: https://github.com/eslint/eslint/blob/master/lib/rules/camelcase.js#L109

[tinymins]

#10554 id-match rule improved.