precommit.md

id	precommit
title	Pre-commit Hook

You can use Prettier with a pre-commit tool. This can re-format your files that are marked as "staged" via git add before you commit.

Option 1. lint-staged

Use Case: Useful for when you want to use other code quality tools along with Prettier (e.g. ESLint, Stylelint, etc.) or if you need support for partially staged files (git add --patch).

Make sure Prettier is installed and is in your devDependencies before you proceed.

npx mrm lint-staged

This will install husky and lint-staged, then add a configuration to the project’s package.json that will automatically format supported files in a pre-commit hook.

See https://github.com/okonet/lint-staged#configuration for more details about how you can configure lint-staged.

Option 2. pretty-quick

Use Case: Great for when you want an entire file formatting on your changed/staged files.

Install it along with husky:

yarn add pretty-quick husky --dev

and add this config to your package.json:

{
  "husky": {
    "hooks": {
      "pre-commit": "pretty-quick --staged"
    }
  }
}

Find more info from here.

Option 3. pre-commit

Use Case: Great when working with multi-language projects.

Copy the following config into your .pre-commit-config.yaml file:

- repo: https://github.com/prettier/prettier
  rev: "" # Use the sha or tag you want to point at
  hooks:
    - id: prettier

Find more info from here.

Option 4. precise-commits

Use Case: Great for when you want partial file formatting on your changed/staged files.

Install it along with husky:

yarn add precise-commits husky --dev

and add this config to your package.json:

{
  "husky": {
    "hooks": {
      "pre-commit": "precise-commits"
    }
  }
}

Note: This is currently the only tool that will format only staged lines rather than the entire file. See more information here

Read more about this tool here.

Option 5. git-format-staged

Use Case: Great for when you want to format partially-staged files, and other options do not provide a good fit for your project.

Git-format-staged is used to run any formatter that can accept file content via stdin. It operates differently than other tools that format partially-staged files: it applies the formatter directly to objects in the git object database, and merges changes back to the working tree. This procedure provides several guarantees:

1. Changes in commits are always formatted.
2. Unstaged changes are never, under any circumstances staged during the formatting process.
3. If there are conflicts between formatted, staged changes and unstaged changes then your working tree files are left untouched - your work won't be overwritten, and there are no stashes to clean up.
4. Unstaged changes are not formatted.

Git-format-staged requires Python v3 or v2.7. Python is usually pre-installed on Linux and macOS, but not on Windows. Use git-format-staged with husky:

yarn add --dev husky prettier git-format-staged

and add this config to your package.json:

{
  "husky": {
    "hooks": {
      "pre-commit": "git-format-staged -f 'prettier --stdin --stdin-filepath \"{}\"' '*.js' '*.jsx' '*.ts' '*.tsx' '*.css' '*.json' '*.gql'"
    }
  }
}

Add or remove file extensions to suit your project. Note that regardless of which extensions you list formatting will respect any .prettierignore files in your project.

To read about how git-format-staged works see Automatic Code Formatting for Partially-Staged Files.

Option 6. bash script

Alternately you can save this script as .git/hooks/pre-commit and give it execute permission:

#!/bin/sh
FILES=$(git diff --cached --name-only --diff-filter=ACMR "*.js" "*.jsx" | sed 's| |\\ |g')
[ -z "$FILES" ] && exit 0

# Prettify all selected files
echo "$FILES" | xargs ./node_modules/.bin/prettier --write

# Add back the modified/prettified files to staging
echo "$FILES" | xargs git add

exit 0

If git is reporting that your prettified files are still modified after committing, you may need to add a post-commit script to update git's index as described in this issue.

Add something like the following to .git/hooks/post-commit:

#!/bin/sh
git update-index -g