small debugging utility
tiny node.js debugging utility modelled after node core's debugging technique.
$ npm install debug
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.
var debug = require'debug''http'http = require'http'name = 'My App';// fake appdebug'booting %s' name;httpcreateServerdebugreqmethod + ' ' + requrl;resend'hello\n';listen3000debug'listening';;// fake worker of some kindrequire'./worker';
var debug = require'debug''worker';setIntervaldebug'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:
On Windows the environment variable is set using the
Then, run the program to be debugged as usual.
When actively developing an application it can be useful to see when the time spent between one
debug() call and the next. Suppose for example you invoke
debug() before requesting a resource, and after as well, the "+NNNms" will show you how much time was spent between calls.
When stdout is not a TTY,
Date#toUTCString() is used, making it more useful for logging the debug information as shown below:
If you're using this in one or more of your libraries, you should use the name of your library so that developers may toggle debugging as desired without guessing names. If you have more than one debuggers you should prefix them with your library name and use ":" to separate features. For example "bodyParser" from Connect would then be "connect:bodyParser".
* character may be used as a wildcard. Suppose for example your library has debuggers named "connect:bodyParser", "connect:compress", "connect:session", instead of listing all three with
DEBUG=connect:bodyParser,connect.compress,connect:session, you may simply do
DEBUG=connect:*, or to run everything using this module simply use
You can also exclude specific debuggers by prefixing them with a "-" character. For example,
DEBUG=*,-connect:* would include all debuggers except those starting with "connect:".
Debug works in the browser as well, currently persisted by
localStorage. Consider the situation shown below where you have
worker:b, and wish to debug both. Somewhere in the code on your page, include:
windowmyDebug = require"debug";
("debug" is a global object in the browser so we give this object a different name.) When your page is open in the browser, type the following in the console:
Refresh the page. Debug output will continue to be sent to the console until it is disabled by typing
myDebug.disable() in the console.
a = debug'worker:a';b = debug'worker:b';setIntervala'doing some work';1000;setIntervalb'doing some work';1200;
Colors are also enabled on "Web Inspectors" that understand the
option. These are WebKit web inspectors, Firefox (since version
and the Firebug plugin for Firefox (any version).
Colored output looks something like:
You can set an alternative logging method per-namespace by overriding the
log method on a per-namespace or globally:
var debug = require'debug';var error = debug'app:error';// by default stderr is usederror'goes to stderr!';var log = debug'app:log';// set this namespace to log via console.loglog.log = console.logbindconsole; // don't forget to bind to console!log'goes to stdout';error'still goes to stderr!';// set all output to go via console.info// overrides all per-namespace log settingsdebug.log = console.infobindconsole;error'now goes to stdout via console.info';log'still goes to stdout, but via console.info now';
- TJ Holowaychuk
- Nathan Rajlich
(The MIT License)
Copyright (c) 2014 TJ Holowaychuk <email@example.com>
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.