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

Thanks @nemesarial! This works like a charm

This does not lint "only staged changes" it lints each file that is changed. Which is annoying because it can block your commit for stuff that isn't even in the commit! Eslint should just have a --diff options like flake8

There is an cleaner way to accomplish this, with husky:

// package.json
...
"husky": {
    "hooks": {
      "pre-commit": "lint-staged"
    }
  },
  "lint-staged": {
    "*.{js,ts,tsx}": [
      "prettier --write",
      "eslint --ext .ts,.tsx,.js --fix"
    ]
  },

@aperkaz

https://www.npmjs.com/package/eslint-plugin-diff

@aperkaz

LGTM, but maybe eslint should be run before prettier.

Note: If you use ESLint, make sure lint-staged runs it before Prettier, not after.
ref: https://prettier.io/docs/en/install.html#git-hooks

There is an cleaner way to accomplish this, with husky:

// package.json
...
"husky": {
    "hooks": {
      "pre-commit": "lint-staged"
    }
  },
  "lint-staged": {
    "*.{js,ts,tsx}": [
      "prettier --write",
      "eslint --ext .ts,.tsx,.js --fix"
    ]
  },

this worked for me & I also took @zhyd1997's suggestion

  },

@aperkaz
Where exactly i need to place above lines inside package.json file.

@Naveen9453 after the dependencies section is a good place, although I tend to locate it at the end of the file. No strict placement requirements though.

package.json configuration of husky no longer works, by design.