In JavaScript, errors can be categorized into several types such as syntax errors, reference errors, type errors, range errors, DOM errors, network errors, and runtime errors. These errors occur due to various reasons like logical errors, unexpected data, or external factors. Effective error handling in JavaScript is crucial for providing a robust user experience. Best practices include using try-catch blocks, being specific with error types, providing descriptive error messages, utilizing the finally block, handling asynchronous errors, and logging errors. By following these guidelines, developers can ensure that their code handles errors gracefully and provides valuable insights for debugging and troubleshooting.