Optimizing database queries is crucial in Node.js to improve application performance. Inefficient queries can lead to slower response times, increased resource consumption, and a poor user experience.

Implementing access restrictions, typically using file permissions, helps secure sensitive static files in Express.js. By restricting who can read or modify these files, you can prevent unauthorized access to sensitive data.

Including a README.md file is essential because it provides valuable information about the package, its usage, and documentation for users and potential contributors. While it's not mandatory, it is considered a best practice to include comprehensive documentation.

Buffer instances in Node.js are fixed in size once allocated, meaning you cannot change their size dynamically. If you need a larger buffer, you would need to create a new one and copy the data if necessary. The other options are not accurate descriptions of buffer behavior in Node.js.

The ESLint rule no-unused-vars helps in identifying variables that are declared but not used in the code. It checks for declared variables that are not referenced elsewhere in the code.

In Node.js, the error event in readable streams is crucial for handling errors that occur during stream processing. When an error occurs while reading or processing data in a readable stream, the error event is emitted, allowing developers to handle and respond to errors appropriately.

In Node.js, the require function is used to load modules. It allows you to include external JavaScript files and use their exported functionalities in your code. It is a fundamental part of Node.js for modular development.

In Node.js, the error in the fs module's callback functions is typically handled by the first parameter, which is conventionally represented by the variable err. Developers check this parameter to determine if an error occurred during a file system operation.

It's advised to mock external dependencies in unit testing to isolate the unit being tested and not rely on the behavior of external services or dependencies. This ensures that unit tests are reliable and that any failures are indicative of issues within the unit itself.

EJS (Embedded JavaScript) is a template engine that uses a tag-based syntax to embed JavaScript code into HTML. This allows developers to include dynamic content and logic directly within HTML templates using <% %> tags. Handlebars, Pug, and Mustache have their own syntax and do not use this tag-based approach.

The primary role of a template engine in web development is to generate dynamic content by combining templates (HTML) with data. Template engines allow developers to insert data into templates, making it easier to create dynamic web pages. Parsing JSON data, creating API endpoints, and executing server-side logic are tasks typically performed by other parts of a web application, not the template engine.

In Node.js, the maximum number of listeners that can be added to an EventEmitter by default is 10. This is to prevent potential memory leaks caused by adding too many listeners inadvertently.