A Claude Code hook to test JS files after an edit or write operation.

settings.json

{
  "hooks": {
    "PostToolUse": [
      {
        "matcher": "Edit|Write",
        "hooks": [
          {
            "type": "command",
            "command": "\"${CLAUDE_PROJECT_DIR}/.claude/hooks/test-file\""
          }
        ]
      }
    ]
  }
}

test-file

#!/usr/bin/env bash

main() {
  local -r filepath="$(jq --raw-output '.tool_input.file_path')"

  if [[ "${filepath}" == *.ts ]]; then
    local test_filepath="${filepath}"

    if [[ "${filepath}" != *.spec.ts ]]; then
      test_filepath="${filepath%.ts}"'.spec.ts'
    fi

    if [[ -f "${test_filepath}" ]] && ! npm test -- "${test_filepath}"; then
      # The Claude Code docs specify to use exit code 2 to indicate an error.
      # This will also print `stderr` to the terminal; whereas other exit
      # codes will not.
      exit 2
    fi
  fi
}

main