The debug npm package is a flexible debugging utility that allows developers to log messages in a structured and conditional way. It is designed to be simple to use and to support modular applications by allowing developers to enable or disable logging on a per-module or per-scope basis.

What are debug's main functionalities?

Conditional Logging

This feature allows developers to create conditional logging statements that can be enabled or disabled based on the namespace. The '%o' formatter can be used to pretty-print objects.

const debug = require('debug')('http');
debug('booting %o', 'My App');
if (error) debug('Error: %o', error);

Namespacing Logs

Namespacing allows developers to categorize logs into different sections, which can be individually toggled on or off. This is useful for separating logs from different parts of an application.

const debug = require('debug');
const log = debug('myapp:log');
const error = debug('myapp:error');
log('This will be logged under the myapp:log namespace');
error('This will be logged under the myapp:error namespace');

Environment Variable Control

The debug package can be controlled using the DEBUG environment variable, which allows developers to specify which namespaces should be logged. This can be set before running the application.

DEBUG=myapp:* node app.js

Browser Support

The debug package also works in the browser. Namespaces can be enabled by setting the debug key in localStorage to the desired namespace.

localStorage.debug = 'myapp:*';

Other packages similar to debug

Readme

Source

debug

tiny node.js debugging utility.

Example

This module is modelled after node core's debugging technique, allowing you to enable one or more topic-specific debugging functions, for example core does the following within many modules:

var debug;
if (process.env.NODE_DEBUG && /cluster/.test(process.env.NODE_DEBUG)) {
  debug = function(x) {
    var prefix = process.pid + ',' +
        (process.env.NODE_WORKER_ID ? 'Worker' : 'Master');
    console.error(prefix, x);
  };
} else {
  debug = function() { };
}

This concept is extremely simple but it works well. With debug you simply invoke the exported function to generate your debug function, passing it a name which will determine if a noop function is returned, or a decorated console.error, so all of the console format string goodies you're used to work fine. A unique color is selected per-function for visibility.

Example app.js:

var debug = require('debug')('http')
  , http = require('http')
  , name = 'My App';

// fake app

debug('booting %s', name);

http.createServer(function(req, res){
  debug(req.method + ' ' + req.url);
  res.end('hello\n');
}).listen(3000, function(){
  debug('listening');
});

// fake worker of some kind

require('./worker');

Example worker.js:

var debug = require('debug')('worker');

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

The DEBUG environment variable is then used to enable these based on space or comma-delimited names. Here are some examples:

License

(The MIT License)

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the 'Software'), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Keywords

FAQs

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Last updated on 29 Nov 2011

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