The default behavior of Express when an error occurs in a middleware is to send a 500 Internal Server Error response. This ensures that the client receives an appropriate error response when something goes wrong in the middleware chain. The other options describe different behaviors that do not occur by default.

The rest operator (...) is used in function parameters to collect all remaining arguments into an array. In the example function myFunction(a, b, ...rest), the ...rest collects any additional arguments passed to the function into an array named rest.

To make the properties of an object immutable in JavaScript, you can use the Object.freeze() method. This method prevents any changes to the object's properties, making them read-only. The other options, Object.preventExtensions() and Object.seal(), allow some level of modification but not full immutability, and Object.makeImmutable() is not a valid method in JavaScript.

When creating a multidimensional array in JavaScript, each element of the main array is a reference to another array or value. This allows for the creation of nested arrays. Changes made to the referenced arrays will affect the main array.

In JavaScript, you can use a while loop to execute a block of code repeatedly as long as a specified condition is true. The for loop is used for iterating over a sequence, and if and switch statements are conditional constructs, not loops.

To schedule a specific action immediately after the current operation completes, you should use process.setImmediate(() => { /* Action code */ });. This ensures that the action is placed in the event queue and executed as soon as possible after the current operation. The other options do not serve this purpose correctly.

In Express.js, static files typically include images, CSS files, and JavaScript files. These files do not change dynamically and can be served directly to clients. HTML files are often dynamically generated, and configuration files are not typically served as static files.

The commonly used configuration file for ESLint is .eslintrc.json. This file allows you to specify ESLint rules, plugins, and other configuration options for your project.

CRUD stands for Create, Retrieve, Update, Delete. These are the four fundamental operations for managing data in a SQL database. Create adds new records, Retrieve reads data, Update modifies existing records, and Delete removes records.

The Events module in Node.js extends the 'EventEmitter' class to allow the creation of event emitter instances. This class provides the functionality for registering event listeners and emitting events.