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Setting ExpressJs

Install Express.js​

To install Express.js using npm, you need Run the following command:

npm install express

This will install the latest version of Express.js and its dependencies in your project's node_modules directory.

Notes

If you want to install a specific version of Express.js, you can use the following command:

npm install express@<version>

Replace <version> with the specific version number you want to install, such as

npm install express@4.17.1

Initial api using express.js​

To create an initial API using Express.js, you can use the following steps:

  • Create a new file called app.js or server.js (or any other name you prefer) in your project's root directory.
  • In your app.js file, require the Express.js module and create an instance of the Express.js application:
app.js
const express = require('express');
const app = express();
  • Define a simple route handler for a GET request that sends a "Hello, World!" response:
app.js
app.get('/', (req, res) => {
  res.send('Hello, World!');
});
  • Start the server and listen for incoming requests:
app.js
app.listen(3000, () => {
  console.log('Server started on port 3000');
});
  • Save the file and run it using the node app.js command in your terminal or command prompt.

This will start the server and listen for incoming requests on port 3000. You can then visit http://localhost:3000 in your web browser to see the "Hello, World!" response.

Note that this is a very basic example and you can define more complex routes and middleware as needed for your API.

Routing in Express.js​

Routing in Express.js refers to the process of mapping HTTP requests to specific handler functions, based on the request's method and URL. Routing is a fundamental aspect of building web applications, as it allows developers to define how their application responds to requests for different resources.

You can define routes using the get, post, put, and delete methods to handle HTTP GET, POST, PUT, and DELETE requests respectively. Here's an example of how to define and use these routes:

const express = require('express');
const app = express();

// GET request
app.get('/', (req, res) => {
  res.send('Hello World!');
});

// POST request
app.post('/', (req, res) => {
  res.send('Got a POST request');
});

// PUT request
app.put('/user', (req, res) => {
  res.send('Got a PUT request at /user');
});

// DELETE request
app.delete('/user', (req, res) => {
  res.send('Got a DELETE request at /user');
});

app.listen(3000, () => {
  console.log('Example app listening on port 3000!');
});

In this example, we define four routes: a GET request at the root path /, a POST request at the root path /, a PUT request at the /user path, and a DELETE request at the /user path.

When a request is made to any of these routes, the corresponding callback function is executed. The callback function takes two parameters: req (the request object) and res (the response object). We can use these objects to read the request data and send a response back to the client.

Note that in order to use the post, put, and delete methods, we need to submit the request using a form or with a tool such as Postman. We cannot make these requests simply by typing a URL into the browser.