OAuth 2.0 is a standard protocol used for securing APIs. It allows you to implement authentication and authorization by issuing tokens to clients. These tokens can be used to access protected resources, making it an effective method for securing RESTful APIs in Express.js applications.

Using a CDN (Content Delivery Network) server is recommended in production environments to serve static files. CDNs distribute static assets across multiple servers located around the world, reducing latency and improving load times for users.

In the package.json file, the scripts property is used to define custom scripts that can be run using npm commands. This property allows you to define various scripts such as "start," "test," or custom scripts for tasks like building, linting, or deploying your application.

You can pass data from your Express route handler to your EJS view using the res.render('view', dataObject); method. This method renders the EJS view and includes the data in the view template, making it accessible for rendering dynamic content. The other options are not valid ways to pass data to EJS views.

In Express.js, a catch-all or wildcard route is used to match any route that has not been matched by earlier routes. This is often used for creating custom error handlers or handling undefined routes.

In Express.js, you can define middleware functions at both the application level and router level. These middleware functions can be used to handle different parts of the request-processing pipeline.

Node.js uses Callbacks to achieve Non-Blocking I/O operations. When a task is completed, a callback function is executed, allowing Node.js to handle many connections simultaneously without blocking the execution of other tasks.

To investigate and resolve differences in package versions, you should start by manually comparing the package.json files in your development and production environments. This will help you identify discrepancies in dependencies and their versions. Option (2) suggests using an alternative package manager, which may not directly address version discrepancies. Option (3) is relevant but doesn't specifically address package version differences. Option (4) is about lockfiles, which can help ensure consistent installations but won't directly highlight version discrepancies.

The do-while loop in JavaScript is used when you want to execute the loop at least once before checking the condition. This is because the condition is checked after the loop body, ensuring that the loop body is executed at least once. The other options do not describe scenarios where a do-while loop is more appropriate.

Using synchronous fs methods can block the event loop in a Node.js application, leading to decreased concurrency and potentially poor performance. It's generally not recommended to use synchronous methods, especially for I/O operations, as they can disrupt the application's responsiveness.

ESLint plugins can be installed and added to the plugins array in the ESLint configuration file. This allows you to extend ESLint's capabilities by adding custom rules or checks to your linting process. The extends option is used to extend or inherit from existing configurations. The rules option is used to configure specific ESLint rules. The overrides option is used for specifying configuration overrides for specific files or directories.

Authentication strategies in web development are used to verify the user's identity. They play a crucial role in ensuring that the users accessing a system or application are who they claim to be. The other options, such as ensuring data integrity and verifying hardware, are not the primary purposes of authentication strategies.