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](https://developer.chrome.com/devtools/docs/console-api#consolelogobject-object) 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 Note that PowerShell using different syntax to set environment variables.
65 $env:DEBUG = "*,-not_this"
68 Then, run the program to be debugged as usual.
72 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.
74 ![](http://f.cl.ly/items/2i3h1d3t121M2Z1A3Q0N/Screenshot.png)
76 When stdout is not a TTY, `Date#toUTCString()` is used, making it more useful for logging the debug information as shown below:
78 ![](http://f.cl.ly/items/112H3i0e0o0P0a2Q2r11/Screenshot.png)
82 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".
86 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=*`.
88 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:".
92 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. You can enable this using `localStorage.debug`:
95 localStorage.debug = 'worker:*'
98 And then refresh the page.
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)
128 By default `debug` will log to stderr, however this can be changed by setting the environment variable `DEBUG_FD` to `1` for stdout and `2` for stderr (the default value).
130 You can also set an alternative logging method per-namespace by overriding the `log` method on a per-namespace or globally:
135 var debug = require('debug');
136 var error = debug('app:error');
138 // by default stderr is used
139 error('goes to stderr!');
141 var log = debug('app:log');
142 // set this namespace to log via console.log
143 log.log = console.log.bind(console); // don't forget to bind to console!
144 log('goes to stdout');
145 error('still goes to stderr!');
147 // set all output to go via console.info
148 // overrides all per-namespace log settings
149 debug.log = console.info.bind(console);
150 error('now goes to stdout via console.info');
151 log('still goes to stdout, but via console.info now');
154 ### Save debug output to a file
156 You can save all debug statements to a file by piping them.
161 $ DEBUG_FD=3 node your-app.js 3> whatever.log
166 By default colors will only be used in a TTY. However this can be overridden by setting the environment variable `DEBUG_COLORS` to `1`.
168 Note: Certain IDEs (such as WebStorm) don't support colors on stderr. In these cases you must set `DEBUG_COLORS` to `1` and additionally change `DEBUG_FD` to `1`.
180 Copyright (c) 2014-2016 TJ Holowaychuk <tj@vision-media.ca>
182 Permission is hereby granted, free of charge, to any person obtaining
183 a copy of this software and associated documentation files (the
184 'Software'), to deal in the Software without restriction, including
185 without limitation the rights to use, copy, modify, merge, publish,
186 distribute, sublicense, and/or sell copies of the Software, and to
187 permit persons to whom the Software is furnished to do so, subject to
188 the following conditions:
190 The above copyright notice and this permission notice shall be
191 included in all copies or substantial portions of the Software.
193 THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND,
194 EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
195 MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
196 IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
197 CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
198 TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
199 SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.