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Debugging with NDB

Getting Started with Debugging Using NDB in Node.js

Modern applications can often be complex, and when things go wrong, it can be difficult to understand where the problem is. This is where debugging comes in. Debugging is the process of identifying, isolating, and fixing problems in code. In Node.js, one of the most powerful debugging tools available is ndb.

ndb is an improved debugging experience for Node.js, enabled by Chrome DevTools. It has some additional features compared to the default Node.js debugger, and in this tutorial, we will guide you through the process of using ndb to debug your Node.js applications.

Installation​

The first step is to install ndb. You can do this globally by using the following command:

npm install -g ndb

This will install ndb globally, so it can be accessed from any project.

Starting a Debugging Session​

Starting a debugging session with ndb is extremely easy. All you need to do is prepend your start script with ndb. For example, if your start script is node index.js, you would start a debugging session with the following command:

ndb node index.js

This will open a new Chrome window with the DevTools interface. From here, you can interact with your application just as you would in the browser.

Setting Breakpoints​

One of the most basic features of any debugger is the ability to set breakpoints. A breakpoint is a specific line of code where the debugger will pause execution, allowing you to inspect the current state of the program.

In ndb, you can set a breakpoint by clicking on the line number in the source code panel. When a breakpoint is set, the line number will be highlighted, and a blue arrow icon will appear.

Stepping Through Code​

Once your code execution is paused at a breakpoint, you can step through your code line by line. This allows you to see the exact flow of your program, and the state of all variables at each step.

  • Step Over: This will execute the current line of code and pause on the next one.
  • Step Into: If the current line of code is a function call, this will "step into" that function and pause on the first line inside it.
  • Step Out: If you're currently inside a function, this will finish the rest of the function and pause on the next line after the function call.

Watching Variables​

ndb allows you to "watch" variables. When a variable is being watched, ndb will display its current value in the Scope panel. This can be extremely useful for understanding how the state of your application changes over time.

To watch a variable, just click on the "Add watch expression" button in the Scope panel, and enter the name of the variable.

Conclusion​

Debugging is a crucial part of software development, and ndb provides a convenient and powerful interface for debugging Node.js applications. With features like easy breakpoint management, step-by-step code execution, and variable watching, ndb can make your debugging sessions much more productive.

Remember, debugging is not just about fixing bugs. It's also an excellent way to understand how your code works, and how different parts of your application interact with each other. So even if your code is working as expected, why not fire up ndb and take a closer look? You might be surprised by what you learn.