3 tiny node.js debugging utility modelled after node core's debugging technique.
13 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.
18 var debug = require('debug')('http')
19 , http = require('http')
24 debug('booting %s', name);
26 http.createServer(function(req, res){
27 debug(req.method + ' ' + req.url);
29 }).listen(3000, function(){
33 // fake worker of some kind
41 var debug = require('debug')('worker');
43 setInterval(function(){
44 debug('doing some work');
48 The __DEBUG__ environment variable is then used to enable these based on space or comma-delimited names. Here are some examples:
50 ![debug http and worker](http://f.cl.ly/items/18471z1H402O24072r1J/Screenshot.png)
52 ![debug worker](http://f.cl.ly/items/1X413v1a3M0d3C2c1E0i/Screenshot.png)
56 On Windows the environment variable is set using the `set` command.
62 Then, run the program to be debugged as ususal.
66 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.
68 ![](http://f.cl.ly/items/2i3h1d3t121M2Z1A3Q0N/Screenshot.png)
70 When stdout is not a TTY, `Date#toUTCString()` is used, making it more useful for logging the debug information as shown below:
72 ![](http://f.cl.ly/items/112H3i0e0o0P0a2Q2r11/Screenshot.png)
76 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".
80 The `*` 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 `DEBUG=*`.
82 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:".
86 Debug works in the browser as well, currently persisted by `localStorage`. Consider the situation shown below where you have `worker:a` and `worker:b`, and wish to debug both. Somewhere in the code on your page, include:
89 window.myDebug = require("debug");
92 ("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:
95 myDebug.enable("worker:*")
98 Refresh the page. Debug output will continue to be sent to the console until it is disabled by typing `myDebug.disable()` in the console.
101 a = debug('worker:a');
102 b = debug('worker:b');
104 setInterval(function(){
105 a('doing some work');
108 setInterval(function(){
109 b('doing some work');
113 #### Web Inspector Colors
115 Colors are also enabled on "Web Inspectors" that understand the `%c` formatting
116 option. These are WebKit web inspectors, Firefox ([since version
117 31](https://hacks.mozilla.org/2014/05/editable-box-model-multiple-selection-sublime-text-keys-much-more-firefox-developer-tools-episode-31/))
118 and the Firebug plugin for Firefox (any version).
120 Colored output looks something like:
122 ![](https://cloud.githubusercontent.com/assets/71256/3139768/b98c5fd8-e8ef-11e3-862a-f7253b6f47c6.png)
126 You can set an alternative logging method per-namespace by overriding the `log` method on a per-namespace or globally:
131 var debug = require('../');
132 var log = debug('app:log');
134 // by default console.log is used
135 log('goes to stdout!');
137 var error = debug('app:error');
138 // set this namespace to log via console.error
139 error.log = console.error.bind(console); // don't forget to bind to console!
140 error('goes to stderr');
141 log('still goes to stdout!');
143 // set all output to go via console.warn
144 // overrides all per-namespace log settings
145 debug.log = console.warn.bind(console);
146 log('now goes to stderr via console.warn');
147 error('still goes to stderr, but via console.warn now');
159 Copyright (c) 2014 TJ Holowaychuk <tj@vision-media.ca>
161 Permission is hereby granted, free of charge, to any person obtaining
162 a copy of this software and associated documentation files (the
163 'Software'), to deal in the Software without restriction, including
164 without limitation the rights to use, copy, modify, merge, publish,
165 distribute, sublicense, and/or sell copies of the Software, and to
166 permit persons to whom the Software is furnished to do so, subject to
167 the following conditions:
169 The above copyright notice and this permission notice shall be
170 included in all copies or substantial portions of the Software.
172 THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND,
173 EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
174 MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
175 IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
176 CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
177 TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
178 SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.