How to make pre-commit clang-format skip over .js files?

I have the following pre-commit hook:

repos:
- repo: https://github.com/pre-commit/mirrors-clang-format
  rev: v14.0.6
  hooks:
  - id: clang-format

While in the past I have seen pre-commit skip over non-CPP files, a coworker just showed me an example with many .js files where it did try to format all of them - resulting in a complete mess.

How do I prevent pre-commit or the clang-format itself from running on these files?

Or preferably just have it only run on certain extensions (.c/.cpp/.h/.hpp/.cxx/etc)

Pre-commit has files but I don't understand how to use it for this (would it be regex?), and I always seem to get something about the formatting wrong. Does it go a nested level under the clang-format line? Or at the same level as it? Or at the uppermost level of "repos"?

Would it just be the following?

repos:
- repo: https://github.com/pre-commit/mirrors-clang-format
  rev: v14.0.6
  hooks:
  - id: clang-format
  files: '(some regex here)'

Solution

pre-commit configurations have two parts -- a providing repo (.pre-commit-hooks.yaml) and a consuming repo (.pre-commit-config.yaml). these configurations have a different format and you can't just paste one of them into the other one blindly

consuming repositories include configurations and code from the remote repository via a repo entry in the .pre-commit-config.yaml

the settings for the clang-format hook you're using in your configuration come from here -- the relevant bits for your question are:

-   id: clang-format
    # ...
    'types_or': [c++, c, c#, cuda, java, javascript, json, objective-c, proto]

filtering by types is outlined in detail in Filtering files with types -- the important parts being:

types, types_or, and files are evaluated together with AND when filtering. Tags within types are also evaluated using AND. ... As with files and exclude, you can also exclude types if necessary using exclude_types.

in your configuration you can either override the value of types_or by setting that on the hook with the same id you're including

repos:
- repo: https://github.com/pre-commit/mirrors-clang-format
  rev: v14.0.6
  hooks:
  - id: clang-format
    types_or: [c++, c]

or you can utilize exclude_types to eliminate them

repos:
- repo: https://github.com/pre-commit/mirrors-clang-format
  rev: v14.0.6
  hooks:
  - id: clang-format
    exclude_types: [javascript, json]

disclaimer: I wrote pre-commit