The main components of Express.js are:

1. Middleware: Middleware functions are functions that have access to the request object (req), the response object (res), and the next middleware function in the application’s request-response cycle. An example of a middleware function is a logger that logs each request to the server.

2. Routing: Routing refers to determining how an application responds to a client request for a specific endpoint, which is a URI (or path) and a specific HTTP request method (GET, POST, and so on). An example of a route in Express is:

app.get(‘/users’, (req, res) => {
res.send(‘This is the users page’);
});

3. Template engine: A template engine enables you to use static template files in your application. The template engine replaces variables in a template file with actual values, and transforms the template into an HTML file sent to the client. Examples of template engines used with Express are Jade, EJS, and Mustache.

4. Error handling: Express has built-in error-handling functions that take care of any errors that might occur in the application. For example, if a route is not found, the Express application can handle the error and send a response to the client with a specific status code and message.

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