Debug Node.js App

In this blog, I am going to cover how to debug a Node.js app.

Introduction

 

In this blog, we are going to see how to debug a node.js app.

 

Previously, in node.js, debugging could be done using the debug command.

 

Note

"Debug" is now deprecated since the latest version. We can use inspect instead.

 

How to use Inspect in node.js

 

Inspect is a completely Graphical User Interface(GUI) based debugger that allows us to enable inspector engine to inspect our application or a script file. By default, it listens to the default port and address:.0.0.1:9229. Still, you can specify your own.

To use inspect, we simply can use the code as below.

node --inspect MyApp.js // Your file name

Well, there are so many command line options available to use. 

 

Using inspect

 

For that, I have created one JavaScript file.

// Using Core node.js package HTTP
var http = require('http');
// Creating HTTP Server
var server = http.createServer(function(req, res) {
   res.writeHead(200);
   res.end('<h1>C#Corner</h1>');
   console.log("Writing In Console !!!");
});
// Specifying Custom Port Number
server.listen(5555);

In this, I am going to print the text in response with port number 5555.

Now, open cmd and just paste the following command.

node inspect MyApp.js

Now, open chrome://inspect/#devices,

 

 

As you can see my script file, MyApp.js, is connected for debugging purposes.

 

Now, let's see how breakpoint works. You need to write it in the console like this.

node --inspect-brk MyApp.js

After execution, all the information will be given to you like this: 

 

 

 

When you open Developer tools window you can see that debugging is already started :

 

 

It always breaks on the first line of the script when using --inspect-brk. So, this way, you can carry on with debugging with node app 

 

With CLI debugger there are plenty of options available,

• cont - for continuation inspecting app or a script
• step - how many steps you want to jump
• next - next statement or breakpoint to be jumped
• out - to step out
• pause - to pause at a specific point.

So this way, you can see how to get started with inspect and with different options.

 

Try it yourself and do let me know if I missed something.