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Express app.listen() Method

Updated on Oct 28, 2024
By Mari Selvan
👁️ 280 - Views
⏳ 4 mins
💬 1 Comment
Express app.listen() Method

Photo Credit to CodeToFun

🙋 Introduction

Express.js provides a straightforward way to create web servers in Node.js, and the app.listen() method is a crucial part of this process.

In this guide, we'll explore the app.listen() method, its syntax, and best practices for starting and configuring your Express.js server.

💡 Syntax

The syntax for the app.listen() method is simple:

syntax.js
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const server = app.listen(port, [hostname], [backlog], [callback])
  • port: The port number on which the server will listen for incoming requests.
  • hostname (optional): The hostname or IP address on which the server will listen. Defaults to 'localhost'.
  • backlog (optional): The maximum length of the queue of pending connections. Defaults to 511.
  • callback (optional): A callback function that is executed once the server is listening.

❓ How app.listen() Works

The app.listen() method binds and listens for connections on the specified host and port. When a client makes a request, the server processes it and sends back the appropriate response.

example.js
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const express = require('express');
const app = express();
const port = 3000;

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

const server = app.listen(port, () => {
  console.log(`Server is running on http://localhost:${port}`);
});

In this example, the server is set up to listen on port 3000, and a callback logs a message once the server is running.

📚 Use Cases

  1. Basic Server Setup:

    Use app.listen() to start a basic server that responds to requests on a specified port.

    example.js
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    const express = require('express');
    const app = express();
    const port = 3000;
    
    app.get('/', (req, res) => {
      res.send('Welcome to my Express server!');
    });
    
    const server = app.listen(port, () => {
      console.log(`Server is running on http://localhost:${port}`);
    });
  2. Dynamic Port Assignment:

    Dynamically assign the port based on the environment variable or use a default value.

    example.js
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    const express = require('express');
    const app = express();
    const port = process.env.PORT || 3000;
    
    app.get('/', (req, res) => {
      res.send('Dynamic Port Assignment');
    });
    
    const server = app.listen(port, () => {
      console.log(`Server is running on http://localhost:${port}`);
    });

🏆 Best Practices

  1. Port Availability Check:

    Check if the specified port is available before calling app.listen() to avoid conflicts.

    example.js
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    const express = require('express');
    const app = express();
    const port = 3000;
    
    const server = app.listen(port, () => {
      console.log(`Server is running on http://localhost:${port}`);
    });
    
    server.on('error', (error) => {
      if (error.code === 'EADDRINUSE') {
        console.error(`Port ${port} is already in use`);
      }
    });
  2. Separate Server Setup:

    Separate the server setup logic from the app.listen() call for better modularity.

    example.js
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    const express = require('express');
    const app = express();
    const port = 3000;
    
    app.get('/', (req, res) => {
      res.send('Separate Server Setup');
    });
    
    const startServer = () => {
      const server = app.listen(port, () => {
        console.log(`Server is running on http://localhost:${port}`);
      });
    };
    
    startServer();
  3. Graceful Shutdown:

    Implement a graceful shutdown mechanism to handle server termination.

    example.js
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    const express = require('express');
    const app = express();
    const port = 3000;
    
    app.get('/', (req, res) => {
      res.send('Graceful Shutdown');
    });
    
    const server = app.listen(port, () => {
      console.log(`Server is running on http://localhost:${port}`);
    });
    
    // Graceful shutdown example
    process.on('SIGTERM', () => {
      server.close(() => {
        console.log('Server gracefully terminated');
        process.exit(0);
      });
    });

🎉 Conclusion

The app.listen() method in Express.js is fundamental for starting your server and listening for incoming requests. By understanding its syntax, examples, and best practices, you can ensure a robust and well-configured Express.js server for your web applications.

Now, go ahead and set up your Express.js server with confidence!

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Author

author
👋 Hey, I'm Mari Selvan

For over eight years, I worked as a full-stack web developer. Now, I have chosen my profession as a full-time blogger at codetofun.com.

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Mari Selvan
Mari Selvan
8 months ago

If you have any doubts regarding this article (Express app.listen() Method), please comment here. I will help you immediately.

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