The primary purpose of using an Object-Relational Mapper (ORM) like Sequelize is to facilitate database interactions by mapping JavaScript objects to database tables. It abstracts the underlying database, making it easier to work with databases and reducing the need for writing raw SQL queries. The other options are not the primary purposes of an ORM.

The Update operation in CRUD (Create, Read, Update, Delete) operations is used to modify existing data in the system. It allows you to make changes to existing records.

The Access-Control-Allow-Methods header in CORS specifies which HTTP methods are allowed for cross-origin requests. It should include a comma-separated list of HTTP methods such as GET, POST, PUT, DELETE, etc.

Improper handling of dependencies and devDependencies can lead to larger bundle sizes when deploying an application. When you include unnecessary dependencies, your application's bundle size increases, impacting load times and performance.

In Express.js, to serve static files, you generally use the static middleware. This middleware allows you to serve files such as images, CSS, and JavaScript to clients.

To optimize the loading of modules in a large-scale application, you should use lazy loading (Option b). Lazy loading allows modules to be loaded only when they are needed, reducing initial load times and improving performance. Minification (Option a) is also a valid optimization technique but may not address the issue of slow initial loading. Increasing server resources (Option c) and reducing the number of modules (Option d) are not effective solutions for optimizing module loading.

In Express.js, an efficient way to handle multiple HTTP methods and optional parameters is to implement a single route handler and use conditional logic to differentiate between methods and handle optional parameters within the handler. This approach minimizes code duplication and keeps your codebase clean and maintainable. Using app.all (Option 1) would capture all HTTP methods and may lead to less control and more complex code. Separating handlers for each combination (Option 2) can result in code redundancy, making it harder to maintain. Creating multiple endpoints (Option 4) can lead to a cluttered route structure.

To avoid memory leaks when multiple loggers are listening to logging events, it's crucial to remove listeners when they are no longer needed. The event.removeListener() method should be used to remove specific listeners, ensuring that you free up memory and resources when loggers are no longer required. The other options are related to listener management but do not directly address memory leaks.

In ESLint, the globals property in the configuration file is used to define global variables that are accessible throughout your code without triggering linting errors. This allows you to specify variables that are declared externally or provided by the environment. The environment option is used to specify which environments your code runs in, but it's not used to define individual global variables. The rules property is used for configuring ESLint rules.

In Jest, you can use the mock function to isolate a module from its dependencies. This allows you to replace the real dependencies with mock implementations for focused unit testing.