Check for `.only` in a Git pre-commit hook. Gives you the option to show the diffs and continue with the commit.

pre-commit

#!/bin/bash

match_pattern=".only"
file_pattern="*.js" 

# Exit if any command fails
set -e

function matching_diff {
  git diff --staged -G "$match_pattern" $@ -- $file_pattern
}

if [ "$(matching_diff)" != "" ]; then

  # Read from stdin to support reading prompts
  exec < /dev/tty

  echo "WARNING! The following files to be committed contain '$match_pattern':"
  matching_diff --name-status

  read -p "==> Show '$match_pattern' matches? [Y/n] " answer

  if [ "$answer" != "n" ]; then
    matching_diff
  fi

  read -p "==> Are you sure you want to continue with your commit? [y/N] " answer

  if [ "$answer" != "y" ]; then
    echo "Halting commit due to presence of '$match_pattern'."
    exit 1
  fi
fi