How to Deploy Express App to Heroku: Step-by-Step Guide

To deploy an Express app to Heroku, first create a Procfile to tell Heroku how to run your app, then push your code to a Heroku Git remote using git push heroku main. Make sure your app listens on the port provided by process.env.PORT and has a start script in package.json.

Syntax

Deploying Express to Heroku involves these key parts:

• Procfile: A file that tells Heroku how to start your app.
• package.json: Must include a start script to run your server.
• Listening on the correct port: Your Express app must use process.env.PORT to work on Heroku.
• Git commands: Use heroku create to make a Heroku app and git push heroku main to deploy.

bash

web: node index.js

Example

This example shows a simple Express app setup ready for Heroku deployment. It listens on the port Heroku assigns and includes a Procfile and package.json with a start script.

javascript

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

const PORT = process.env.PORT || 3000;

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

app.listen(PORT, () => {
  console.log(`Server running on port ${PORT}`);
});

Output

Server running on port 3000 (or assigned Heroku port)

Common Pitfalls

Common mistakes when deploying Express to Heroku include:

• Not using process.env.PORT for the server port, causing the app to crash on Heroku.
• Missing a start script in package.json, so Heroku doesn't know how to run the app.
• Forgetting to commit the Procfile or having wrong syntax in it.
• Not pushing to the correct Heroku Git remote branch.

javascript

Wrong (hardcoded port):
const PORT = 3000;

Right (dynamic port):
const PORT = process.env.PORT || 3000;

Quick Reference

• Create a Heroku app: heroku create
• Add a Procfile with: web: node index.js
• Ensure package.json has: "start": "node index.js" script
• Use process.env.PORT in your Express app
• Deploy with: git push heroku main

Key Takeaways

Always use process.env.PORT to listen on the correct port for Heroku.

Include a start script in package.json to tell Heroku how to run your app.

Create a Procfile with 'web: node index.js' to define the web process.

Use git push heroku main to deploy your code to Heroku.

Check for common mistakes like missing Procfile or hardcoded ports.