How to use nodejs

Node.js is a JavaScript runtime environment that runs on the server side and can parse and execute JavaScript code. Node.js is easy to get started because JavaScript is one of the most popular programming languages ​​in the world, and Node.js has huge community support and constantly updated documentation resources. This article explains how to install and use Node.js.

Installation Node.js

Node.js installation is simple. First, you need to go to the official website of Node.js [https://nodejs.org](https://nodejs.org) to download the installation package suitable for your computer operating system. Different operating systems have different installation methods. Here we take Windows system as an example.

On the official website download page, select the latest version of the Node.js installation package. After downloading, open the installation package and follow the wizard steps to complete the installation step by step. After the installation is complete, you can open a command prompt or terminal and enter the following command:

node -v

If Node.js is installed successfully, the version number of Node.js should be output.

Create your first Node.js application

Generally, people use Node.js to develop web applications. Here's how to create a simple HTTP server.

Open the editor, create a new folder, name it myapp, and create a new index.js file in the folder. Enter the following code in the index.js file:

const http = require('http');

const hostname = '127.0.0.1';
const port = 3000;

http.createServer((req, res) => {
  res.statusCode = 200;
  res.setHeader('Content-Type', 'text/plain');
  res.end('Hello World
');
}).listen(port, hostname, () => {
  console.log(`Server running at http://${hostname}:${port}/`);
});

The code is explained as follows:

1. First, use the require() method to introduce the http module that comes with Node.js. This module uses Used to create HTTP servers and handle HTTP requests.
2. Define the server host name and port number.
3. Use the http.createServer() method to create an HTTP server and pass in a callback function for the server.
4. In the callback function, set the status code and header information of the HTTP response, and use the res.end() method to set the response body information.
5. Finally, use the server's listen() method to start the server and output the startup success message to the command line window.

Save the file, open the command prompt or terminal, switch to the myapp directory, and execute the following command:

node index.js

If everything is normal, you should see the output "Server running" on the command line at http://127.0.0.1:3000/" information. Open a browser and visit this address, you should see "Hello World" output.

Node.js module

In Node.js, a module is the most basic unit for defining shared functions. These shared functions include variables, functions, objects, etc. Node.js has a large number of built-in modules and also supports the use of third-party modules.

The main modules of Node.js include:

• http: module to create HTTP servers and handle HTTP requests.
• fs: File system module, used for file reading, writing, modification, deletion and other operations.
• path: Path module, used to process and convert strings of file paths.

Node.js modules are introduced through the require() method, for example:

const http = require('http');

Using third-party modules

Node.js has hundreds of third-party modules , which can easily meet the needs of the application. The method of using third-party modules is as follows:

1. Use the npm command to install the module

   npm is the built-in package management tool of Node.js, which can easily install and manage Node. js module. The npm module library contains a large number of modules. You can search for the required modules in [https://www.npmjs.com/](https://www.npmjs.com/).

   The command to install the module is:

   npm install <module_name>

2. Use the require() method to introduce the module

   After downloading and installing, you can use require( ) method to introduce the module, for example:

   const express = require('express');

3. Use the functions provided by third-party modules

   The downloaded and installed module will contain some interfaces and functions provided by itself. By introducing modules and using corresponding methods and properties, you can use the functions provided by third-party modules.

   For example, when using the Express framework, you can create a web application through the following code:

   const express = require('express');
   const app = express();
   
   app.get('/', (req, res) => {
     res.send('Hello World!');
   });
   
   app.listen(3000, () => {
     console.log('Example app listening on port 3000!');
   });

   The above is a brief introduction and usage of Node.js. Learning Node.js requires more practice and coding, and experience the powerful functions of JavaScript on the server side.

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