Git pre-comit hook to lint files using npm

pre-commit

#!/usr/bin/env sh

# This loads nvm
export NVM_DIR="$([ -z "${XDG_CONFIG_HOME-}" ] && printf %s "${HOME}/.nvm" || printf %s "${XDG_CONFIG_HOME}/nvm")"
[ -s "$NVM_DIR/nvm.sh" ] && \. "$NVM_DIR/nvm.sh"

# Bypass if a merge is happening
function skipIfMerging() {
  local isMerge="$(git rev-parse -q --verify MERGE_HEAD)"
  # If isMerge is a hash, a merge is ongoing
  if [[ ! -z "$isMerge" ]]; then
    exit 0
  fi
}

function stagedFiles() {
  # Get staged files by extension
  local files=$(git diff-index --cached --name-only HEAD | grep ".*\.$1$")
  # Join lines by whitespace
  files=$(echo $files | tr '\n' ' ')
  # Trim last whitespace character
  files=$(echo $files | xargs)
  echo "$files"
}

function lintFiles() {
  local type=$1
  # Command to run from a local or remote npm package
  local bin="npx $2"
  local args=$3
  # Shifts all the positional arguments down by three
  shift; shift; shift
  # $@ is all the arguments
  if [[ ! -z "$@" ]]; then
    echo -e "\033[33mLinting $type files...\033[0m"
    # Invoke npm bin+binary with the staged files
    echo "$@" | xargs $bin $args
    # $? is the output of the last command
    if [[ ! "$?" == 0 ]]; then
      PASS=false
    fi
  fi
}

skipIfMerging
PASS=true

STAGED_CSS=$(stagedFiles "scss")
if [[ ! -z "$STAGED_CSS" ]]; then
    lintFiles CSS stylelint "--allow-empty-input" $STAGED_CSS
fi

STAGED_JS=$(stagedFiles "jsx\?")
if [[ ! -z "$STAGED_JS" ]]; then
    lintFiles JS eslint "--no-error-on-unmatched-pattern --color" $STAGED_JS
fi

if ! $PASS; then
  echo -e "\033[41m\033[1mCOMMIT FAILED:\033[0m \033[1mYour commit contains files that did not pass the linter check. Please fix the errors and try again.\033[0m\n"
  exit 1
fi

exit $?