Git Hook – npm install if package.json is Modified

Most of the projects I work on these days contain a frequently-modified package.json file to manage dependencies.  You would think by know I'd be used seeing the package.json file when I did a git pull and it would trigger something in my head to execute npm install to ensure I had the latest dependencies installed but I somehow continue to forget to do so.  Instead I see npm start  result in errors which leads to facepalm after facepalm.  It's probably time to automate this task.

A quick Google search led me to a series of gists to use a git hook to trigger npm install if a package.json file has been updated. Place a post-merge file in your .git/hooks directory with the following contents:

#/usr/bin/env bash
# MIT © Sindre Sorhus - sindresorhus.com

# git hook to run a command after `git pull` if a specified file was changed
# Run `chmod +x post-merge` to make it executable then put it into `.git/hooks/`.

changed_files="$(git diff-tree -r --name-only --no-commit-id ORIG_HEAD HEAD)"

check_run() {
	echo "$changed_files" | grep --quiet "$1" && eval "$2"
}

# Example usage
# In this example it's used to run `npm install` if package.json changed and `bower install` if `bower.json` changed.
check_run package.json "npm install"
check_run bower.json "bower install"

Reading down the comments in the gist show a number of other useful conditional triggers, like PHP's composer install, preprocessing of .sass files, and more.

# Updating git submodules
check_run .gitmodules "git submodule init && git submodule update"

# Installing composer dependencies
check_run composer.json "composer install"

# For those who use gulp
check_run web/assets "gulp --production"

This hook will be incredibly useful for me moving forward -- no more needing to remember steps I need to execute upon every pull!