The main components of Express.js are:

1. Router: This is the Express.js component that handles the routing of incoming requests to the appropriate controller. For example, a request to ‘/users’ might be routed to a ‘usersController’ to handle the request.

2. Middleware: This is the component that allows you to intercept requests and modify the request or response before it reaches the controller. For example, you might use middleware to authenticate a user before they can access a certain route.

3. Request and Response objects: These objects are used to pass information between the server and the client. The request object contains information about the incoming request, such as the HTTP method, the URL, and any data that was sent with the request. The response object is used to send data back to the client.

4. Templating Engine: This component allows you to render dynamic HTML pages based on data from the server. For example, you might use a templating engine to render a list of users from a database.

5. Error Handling: This component allows you to handle errors that occur during the request/response cycle. For example, you might use error handling to catch a database error and display an appropriate error message to the user.

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