Pre-commit hook for linting JS with ESLint before committing

pre-commit-eslint

#!/bin/sh

STAGED_FILES=$(git diff --cached --name-only --diff-filter=ACM | grep -v "^node_modules/" | grep ".jsx\{0,1\}$")
ESLINT="$(git rev-parse --show-toplevel)/node_modules/.bin/eslint"

if [[ "$STAGED_FILES" = "" ]]; then
  exit 0
fi

PASS=true

# provide notice that linting is in progress, can be quite slow
echo "\nLinting JavaScript..."

# check for ESLint
if [[ ! -x "$ESLINT" ]]; then
  echo "\033[41m\`node_modules/.bin/eslint\` not found\033[0m have you run \`npm install\`?\n"
  exit 1
fi

# run all staged JS/JSX files through ESLint
for FILE in $STAGED_FILES
do
  "$ESLINT" "$FILE"

  if [[ "$?" != 0 ]]; then
    PASS=false
  fi
done

# provide result
if ! $PASS; then
  echo "\n\033[41mCommit Failed\033[0m Your commit contains files that should pass ESLint but do not. Please fix the ESLint errors and try again.\n"
  exit 1
else
  echo "Linting OK\n"
fi

exit $?

This is a variant of a script I found by shettyrahul8june.

Main changes were to reduce the amount of output for my personal preferences (I just wanted to know it was in progress and ESLint was already returning detailed errors for each problem including a filename).

I also added a filter for node_modules from the staged files because of an internal company policy to commit the node_modules folder and, even though ESLint is set to ignore it, it slows the hook process down attempting and error'ing them.