To ensure high-quality code when you hire ReactJS developers, conduct a thorough vetting process. Look for developers who follow best coding practices, such as writing modular, reusable components and adhering to the DRY (Don’t Repeat Yourself) principle. Request code samples or previous project portfolios to assess their coding style and problem-solving abilities. Additionally, test their proficiency in using debugging and testing tools like React Developer Tools, Jest, or Enzyme to ensure they can identify and fix issues quickly. Regular code reviews and unit testing will further ensure the quality of the code.