Debugging Express

Applications generated by express

The debug module is used by an express command-generated application, and its debug namespace is scoped to the application's name.

For example, if you used $ express sample-app to create the app, you can use the following command to activate the debug statements:

$ DEBUG=sample-app:* node ./bin/www

You can assign a comma-separated list of names to indicate more than one debug namespace:

$ DEBUG=http,mail,express:* node index.js

Environment Variables

When using Node.js, you may change the behavior of the debug logging by setting a few environment variables:

Note that environment variables that begin with DEBUG_ are transformed into an Options object that can be utilized with %o/%O formatters. The whole list may be found in the util.inspect() documentation in Node.js.

Formatters

Printf-style formatting is used by Debug. The following formatters are officially supported:

Custom formatters

By extending the debug. formatters object, you can add custom formatters. If you wanted to add support for rendering a Buffer as hex with %h, for example, you could do something like this:

const createDebug = require('debug')
createDebug.formatters.h = (v) => {
  return v.toString('hex')
}

// …elsewhere
const debug = createDebug('foo')
debug('this is hex: %h', new Buffer('hello world'))
//   foo this is hex: 68656c6c6f20776f726c6421 +0ms

Checking if a debug target is enabled or not

You can check whether a debug instance is enabled after you've created it by looking at the enabled property:

const debug = require('debug')('http');

if (debug.enabled) {
  // do stuff...
}
 

You may also manually toggle this option to enable or disable the debug instance.

Browser Support

You can use browserify to create a browser-ready script, or you can utilize the browserify-as-a-service build if you don't want to do it yourself.

The enabling status of Debug is currently saved in localStorage. Consider the following scenario: you have two workers, worker: a and worker: b, and you want to debug them both. You can use localStorage.debug to enable this:

localStorage.debug = 'worker:*'

Then go back to the website and reload it.

a = debug('worker:a');
b = debug('worker:b');

setInterval(function(){
  a('doing some work');
}, 1000);

setInterval(function(){
  b('doing some work');
}, 1200)

Refer to know about :  What is debugging

Frequently Asked Questions

1. What is debugging express?

Express logs information about route matching, middleware functions, application mode, and other things using the Debug module.

Set the DEBUG environment variable to Express to access all internal logs utilized by Express while launching the app-

DEBUG = express:* node index.js 

2. In an Express.js app, how do you enable debugging?

Debugging in an Express.js app can be enabled in a variety of ways depending on the operating system.

On Linux, use the following command:

DEBUG=express:* node app.js DEBUG=express:* node app.js
 

On Windows, type the following command:

set DEBUG=*node app.js DEBUG=*node app.js DEBUG=*node app.js

Also see :  usb debugging

Key takeaways

In this blog, we learned Debugging in the express and got to know that Simply supply the name of your module to the debug function, and it will return a decorated version of the console. You can use this error to pass debug statements. This allows you to activate debug output for certain areas of your module as well as the entire module.

Learn more, wget command in linux

A colour is assigned to each debug instance based on its namespace name. 

You can learn more about Express and Express router before directly diving into debugging.