Git Hooks

Git Hooks

Git hooks are scripts that run automatically at specific points in the Git workflow — before a commit, after a merge, before a push, and more. They’re stored in .git/hooks/.

Hook Types

Hook	Trigger	Common Uses
pre-commit	Before committing	Run linter, format code, check for secrets
commit-msg	After commit message is written	Validate message format
prepare-commit-msg	Before message editor opens	Prepend issue number
post-commit	After commit is created	Notify, trigger CI locally
pre-push	Before push	Run tests
pre-rebase	Before rebase	Safety checks

Writing a Hook

Hooks are executable scripts in .git/hooks/. Create pre-commit:

.git/hooks/pre-commit

#!/bin/sh
# Run ESLint on staged TypeScript files
STAGED=$(git diff --cached --name-only --diff-filter=ACM | grep '\.ts$')

if [ -n "$STAGED" ]; then
  npx eslint $STAGED
  if [ $? -ne 0 ]; then
    echo "ESLint failed — fix errors before committing"
    exit 1
  fi
fi

# Make it executable
chmod +x .git/hooks/pre-commit

Husky (Shareable Hooks)

The problem with raw Git hooks: .git/hooks/ isn’t committed. Husky stores hooks in the repo and registers them via npm prepare.

npm install -D husky
npx husky init

This creates a .husky/ directory and a prepare script in package.json.

pre-commit with lint-staged

Only lint the files that are staged (not the whole project):

npm install -D lint-staged

.husky/pre-commit:

npx lint-staged

package.json:

{
  "lint-staged": {
    "*.{ts,tsx}": ["eslint --fix", "prettier --write"],
    "*.{js,jsx}": ["eslint --fix"],
    "*.{css,scss}": ["prettier --write"]
  }
}

commit-msg — Enforce Conventional Commits

npm install -D @commitlint/cli @commitlint/config-conventional

commitlint.config.js:

export default { extends: ['@commitlint/config-conventional'] };

.husky/commit-msg:

npx --no -- commitlint --edit $1

Now commit messages must follow the format:

feat: add user authentication
fix: resolve null pointer in payment
chore: upgrade dependencies
docs: update API reference

pre-push — Run Tests

.husky/pre-push:

#!/bin/sh
npm test

Skipping Hooks

# Skip hooks for a commit (use sparingly — breaks CI guarantees)
git commit --no-verify -m "Emergency fix"
git push --no-verify

Hook Examples

Check for debug statements

#!/bin/sh
# .husky/pre-commit — find leftover console.log / debugger

if git diff --cached | grep -E '^\+.*(console\.log|debugger)' > /dev/null; then
  echo "Found console.log or debugger in staged changes."
  exit 1
fi

Prepend branch name to commit message

.husky/prepare-commit-msg

#!/bin/sh
BRANCH=$(git symbolic-ref --short HEAD)
JIRA=$(echo $BRANCH | grep -oE 'PROJ-[0-9]+')

if [ -n "$JIRA" ]; then
  sed -i "1s/^/$JIRA: /" "$1"
fi

Conventional Commits

A commit message specification:

<type>(<scope>): <description>

[optional body]

[optional footer]

Types: feat, fix, docs, style, refactor, test, chore, perf

Benefits:

• Automated changelog generation
• Semantic version bumping
• Clear commit history
• Better PR reviews