An example of a Node.js project that utilizes the npm package Husky and git hooks for automatic execution of npm install (or yarn) after git merge, git checkout or git rebase, if needed.

Example video

1. Install husky: npm install --save-dev husky

2. Copy and use the relevant scripts from this repository for npm (./githooks/npm/) or yarn (./githooks/yarn/).

3. In package.json, add the git hooks using husky:

   {
    ...
    "husky": {
    "hooks": {
    "post-checkout": "./githooks/npm/post-checkout.sh $HUSKY_GIT_PARAMS",
    "post-merge": "./githooks/npm/post-merge.sh"
    }
    }
   }

Both scripts (post-checkout.sh & post-merge.sh) use git diff in order to find which files have been updated by comparing two commits. Then, by using grep, the scripts check if package-lock.json (for npm) or yarn.lock (for yarn) are among the updated files.

• For merge: git diff HEAD^ HEAD - compare the previous commit (HEAD^) with the current commit (HEAD). We compare these commits because git merge creates a new commit of the merge itself.

• For checkout: We use the enivronment variable provided by husky $HUSKY_GIT_PARAMS in the post-checkout.sh script in order to provide git diff the source & target commits (of the source & target branches, respectively).

• For rebase: git checkout is executed as part of git rebase, so post-checkout.sh is executed in this scenario.

Flags used:

• git diff --name-only
  • --name-only - Show only the names of the changed files.
• grep -x -q
  • -x - Select only matches that exactly match the whole line.
  • -q - Do not write anything to standard output, but only return the exit status code.