Exploring Longjohn: Comprehensive API for Node.js and Error Handling

Longjohn is a powerful library in Node.js known for enhancing error-handling capabilities. It provides
clear and structured stack traces for better debugging and troubleshooting during development.
This blog post will introduce Longjohn and cover a variety of its APIs with practical code snippets.

Getting Started with Longjohn

  
    const longjohn = require('longjohn');
    longjohn.async_trace_limit = 20; // Set the async call chain length
  

Initial Setup

  
    const longjohn = require('longjohn');
  

This sets up Longjohn in your Node.js application.

Setting Async Call Chain Length

  
    longjohn.async_trace_limit = 10;
  

This sets the limit for the asynchronous call chain. The default is 10.

Example: Logging Errors with Longjohn

  
    process.on('uncaughtException', function (err) {
      console.log('Caught exception: ' + err.stack);
    });
    
    setTimeout(function() {
      // Intentionally cause an error
      nonExistentFunction();
    }, 1000);
  

Use the uncaughtException event to log errors with enhanced stack traces.

Disable Longjohn

  
    longjohn.async_trace_limit = -1; // Disables Longjohn
  

This is particularly useful for turning off Longjohn in production environments.

Practical App Example

Let’s create a basic Express application integrated with Longjohn for better debugging.

Step 1: Install Dependencies

  
    npm install express longjohn
  

Step 2: Create a Simple Express App

  
    const express = require('express');
    const longjohn = require('longjohn');
    
    longjohn.async_trace_limit = 10;
    
    const app = express();
    
    app.get('/', (req, res) => {
      res.send('Hello World!');
    });

    app.get('/error', (req, res) => {
      nonExistentFunction(); // This will cause an error for demonstration
      res.send('This will not be printed');
    });
    
    app.listen(3000, () => {
      console.log('Server is running on port 3000');
    });

    process.on('uncaughtException', function (err) {
      console.error('Caught exception:', err.stack);
    });
  

Access the App

Run the app with node app.js and navigate to http://localhost:3000/ for the home route and http://localhost:3000/error to trigger an error.

With the integration of Longjohn, you will see detailed stack traces in the console output that greatly assist in pinpointing the source of errors.

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