Pre-commit hook for eslint, linting *only* staged changes.

pre-commit.sh

#!/bin/bash

for file in $(git diff --cached --name-only | grep -E '\.(js|jsx)$')
do
  git show ":$file" | node_modules/.bin/eslint --stdin --stdin-filename "$file" # we only want to lint the staged changes, not any un-staged changes
  if [ $? -ne 0 ]; then
    echo "ESLint failed on staged file '$file'. Please check your code and try again. You can run ESLint manually via npm run eslint."
    exit 1 # exit with failure status
  fi
done

Thanks. Very helpful.

Option --diff-filter=d should be specified in git diff to exclude deleted files.

@Fer0x Where would that go?

@Alberth8 It'd be like this -> git diff --diff-filter=d --cached --name-only

Thanks @dahjelle! Great stuff :)

Thank you very much

eslint is quite slow when it runs against my entire project, this is much faster, thanks!!

Has anyone figured out a workflow for using the --fix flag during this pre-commit hook?

What I've come across is that when the pre-commit hook is triggered for files that are staged, the new changes aren't included in the commit.

It makes sense why it wouldn't be included: this is changing a staged file, and those changes would also have to be staged.

lint-staged has a partly-working fix for this, however, and as they note, this doesn't work for partially-staged files, AKA files whose changes have been cherry-picked for a commit.

@SalTor take a look at this. It works well for me.

Thank you very much.

One-liner version of the above:

git diff --diff-filter=d --cached --name-only | grep -E '\.(js|jsx)$' | xargs -I % sh -c 'git show ":%" | eslint --stdin --stdin-filename "%";'

you can do this in one line git diff --cached --name-only | grep ".js$" | xargs ./node_modules/.bin/eslint

nice, @richistron

@jancimajek's one-liner is great but does not handle spaces (and other funny chars) in the filename. Using git diff -z with xargs -0 handles that nicely: luuuis/pre-commit.sh.

The @richistron one liner will lint the changed files in the local checkout, which is not necessarily what is being committed to Git if you have not staged every hunk in a file.

thanks

Thanks @dahjelle.

The scripts above works well enough for a handful of changes, but for large projects when things like a project-wide search & replace is performed, it takes ages because the files are sent one by one to eslint. Running over the whole project only takes 20 seconds, but the commit hook takes 4 minutes! Is there a way to batch the files instead of calling eslint for every file one by one?

This is great! @lifenstein That seems like a less common case, so when it happens you could run git commit --no-verify to skip the 4 minute check and then run eslint directly. For most commits this will be much faster than linting the entire project every time.

One-liner version of the above:

git diff --diff-filter=d --cached --name-only | grep -E '\.(js|jsx)$' | xargs -I % sh -c 'git show ":%" | eslint --stdin --stdin-filename "%";'

I had to change the @jancimajek version a little bit, because % is reserved in my shell and eslint is not global, so:

git diff --diff-filter=d --cached --name-only | grep -E '\.(js|jsx)$' | xargs -I A sh -c 'git show ":A" | .\\node_modules\\.bin\\eslint --stdin --stdin-filename "A";'

Thank you to OP -- very useful. I adapted and my lint-staged.sh file looks like this:

#!/bin/bash
clear
fileList=$(git diff --diff-filter=d --cached --name-only | grep -E '\.(js|vue)$')
if [ ${#fileList} -lt 1 ]; then
    echo -e "You have no staged .js or .vue files to test\n"
    exit
fi
npx eslint ${fileList[*]} "$@"
if [ $? -ne 0 ]; then
    echo -e "\nPlease fix the above linting issues before committing.\n"
    exit 1
fi

Benefits are:

• using npx allows running local or global eslint
• Passing the file list to eslint limits this to a single run -- so eslint only has to start up once, and not once for every file
• It only exits after all staged files have been tested
• Has an out for when no files are staged
• allows you to configure eslint by adding arguments to shell command. ie. ./lint-staged.sh --fix