Introduction to Longjohn

Longjohn is a powerful utility for Node.js that simplifies the debugging process by providing detailed stack traces for your application. This tool is invaluable for developers who need to track errors and optimize their code efficiently. In this blog, we will explore Longjohn and its multitude of APIs with practical examples to help you get the most out of this robust debugging tool.

Getting Started with Longjohn

To get started with Longjohn, you need to install it using npm:

npm install longjohn

Basic Usage

Once installed, you can start using Longjohn by requiring it in your Node.js application:

require('longjohn');

Here’s a basic example of how you can use Longjohn to get detailed stack traces:

 const longjohn = require('longjohn');
function problematicFunction() {
  setTimeout(() => {
    throw new Error("Something went wrong!");
  }, 1000);
}
problematicFunction(); 

Advanced Configuration

Longjohn provides APIs to customize its behavior. Here are some advanced configurations:

 longjohn.async_trace_limit = 10;  // limits the number of async traces to 10 longjohn.empty_frame_url   = 'no_stack.html';  // URL to load when a callstack is empty 

Integration with Applications

Let’s create a simple Node.js application to demonstrate how Longjohn can be integrated:

 const express = require('express'); const longjohn = require('longjohn');
const app = express();
longjohn.async_trace_limit = 5;
app.get('/', (req, res) => {
  req.context.getUser()
    .then(user => res.send(user))
    .catch(err => {
      console.error('Error occurred:', err);
      res.status(500).send('Internal Server Error');
    });
});
app.listen(3000, () => {
  console.log('Server is running on http://localhost:3000');
}); 

In this example, we set an async trace limit of 5 to manage the length of stack traces. This ensures we get sufficient information while avoiding overly verbose outputs.

Conclusion

Longjohn is an excellent tool for easing the debugging process in Node.js applications by providing meaningful and detailed stack traces. The above examples and configurations should help you get started and adapt Longjohn to your specific needs.

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