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 usual.
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('debug');
132 var error = debug('app:error');
134 // by default stderr is used
135 error('goes to stderr!');
137 var log = debug('app:log');
138 // set this namespace to log via console.log
139 log.log = console.log.bind(console); // don't forget to bind to console!
140 log('goes to stdout');
141 error('still goes to stderr!');
143 // set all output to go via console.info
144 // overrides all per-namespace log settings
145 debug.log = console.info.bind(console);
146 error('now goes to stdout via console.info');
147 log('still goes to stdout, but via console.info now');
150 ### Save debug output to a file
152 You can save all debug statements to a file by piping them.
157 $ DEBUG_FD=3 node your-app.js 3> whatever.log
169 Copyright (c) 2014 TJ Holowaychuk <tj@vision-media.ca>
171 Permission is hereby granted, free of charge, to any person obtaining
172 a copy of this software and associated documentation files (the
173 'Software'), to deal in the Software without restriction, including
174 without limitation the rights to use, copy, modify, merge, publish,
175 distribute, sublicense, and/or sell copies of the Software, and to
176 permit persons to whom the Software is furnished to do so, subject to
177 the following conditions:
179 The above copyright notice and this permission notice shall be
180 included in all copies or substantial portions of the Software.
182 THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND,
183 EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
184 MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
185 IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
186 CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
187 TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
188 SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.