node_modules/debug/README.md

   1 # debug
   2 [![Build Status](https://travis-ci.org/visionmedia/debug.svg?branch=master)](https://travis-ci.org/visionmedia/debug)  [![Coverage Status](https://coveralls.io/repos/github/visionmedia/debug/badge.svg?branch=master)](https://coveralls.io/github/visionmedia/debug?branch=master)  [![Slack](https://visionmedia-community-slackin.now.sh/badge.svg)](https://visionmedia-community-slackin.now.sh/) [![OpenCollective](https://opencollective.com/debug/backers/badge.svg)](#backers)
   3 [![OpenCollective](https://opencollective.com/debug/sponsors/badge.svg)](#sponsors)
   4
   5
   6
   7 A tiny node.js debugging utility modelled after node core's debugging technique.
   8
   9 **Discussion around the V3 API is under way [here](https://github.com/visionmedia/debug/issues/370)**
  10
  11 ## Installation
  12
  13 ```bash
  14 $ npm install debug
  15 ```
  16
  17 ## Usage
  18
  19 `debug` exposes a function; simply pass this function the name of your module, and it will return a decorated version of `console.error` for you to pass debug statements to. This will allow you to toggle the debug output for different parts of your module as well as the module as a whole.
  20
  21 Example _app.js_:
  22
  23 ```js
  24 var debug = require('debug')('http')
  25   , http = require('http')
  26   , name = 'My App';
  27
  28 // fake app
  29
  30 debug('booting %s', name);
  31
  32 http.createServer(function(req, res){
  33   debug(req.method + ' ' + req.url);
  34   res.end('hello\n');
  35 }).listen(3000, function(){
  36   debug('listening');
  37 });
  38
  39 // fake worker of some kind
  40
  41 require('./worker');
  42 ```
  43
  44 Example _worker.js_:
  45
  46 ```js
  47 var debug = require('debug')('worker');
  48
  49 setInterval(function(){
  50   debug('doing some work');
  51 }, 1000);
  52 ```
  53
  54  The __DEBUG__ environment variable is then used to enable these based on space or comma-delimited names. Here are some examples:
  55
  56   ![debug http and worker](http://f.cl.ly/items/18471z1H402O24072r1J/Screenshot.png)
  57
  58   ![debug worker](http://f.cl.ly/items/1X413v1a3M0d3C2c1E0i/Screenshot.png)
  59
  60 #### Windows note
  61
  62  On Windows the environment variable is set using the `set` command.
  63
  64  ```cmd
  65  set DEBUG=*,-not_this
  66  ```
  67
  68  Note that PowerShell uses different syntax to set environment variables.
  69
  70  ```cmd
  71  $env:DEBUG = "*,-not_this"
  72   ```
  73
  74 Then, run the program to be debugged as usual.
  75
  76 ## Millisecond diff
  77
  78   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.
  79
  80   ![](http://f.cl.ly/items/2i3h1d3t121M2Z1A3Q0N/Screenshot.png)
  81
  82   When stdout is not a TTY, `Date#toUTCString()` is used, making it more useful for logging the debug information as shown below:
  83
  84   ![](http://f.cl.ly/items/112H3i0e0o0P0a2Q2r11/Screenshot.png)
  85
  86 ## Conventions
  87
  88   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".
  89
  90 ## Wildcards
  91
  92   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=*`.
  93
  94   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:".
  95
  96 ## Environment Variables
  97
  98   When running through Node.js, you can set a few environment variables that will
  99   change the behavior of the debug logging:
 100
 101 | Name      | Purpose                                         |
 102 |-----------|-------------------------------------------------|
 103 | `DEBUG`   | Enables/disables specific debugging namespaces. |
 104 | `DEBUG_COLORS`| Whether or not to use colors in the debug output. |
 105 | `DEBUG_DEPTH` | Object inspection depth. |
 106 | `DEBUG_SHOW_HIDDEN` | Shows hidden properties on inspected objects. |
 107
 108
 109   __Note:__ The environment variables beginning with `DEBUG_` end up being
 110   converted into an Options object that gets used with `%o`/`%O` formatters.
 111   See the Node.js documentation for
 112   [`util.inspect()`](https://nodejs.org/api/util.html#util_util_inspect_object_options)
 113   for the complete list.
 114
 115 ## Formatters
 116
 117
 118   Debug uses [printf-style](https://wikipedia.org/wiki/Printf_format_string) formatting. Below are the officially supported formatters:
 119
 120 | Formatter | Representation |
 121 |-----------|----------------|
 122 | `%O`      | Pretty-print an Object on multiple lines. |
 123 | `%o`      | Pretty-print an Object all on a single line. |
 124 | `%s`      | String. |
 125 | `%d`      | Number (both integer and float). |
 126 | `%j`      | JSON. Replaced with the string '[Circular]' if the argument contains circular references. |
 127 | `%%`      | Single percent sign ('%'). This does not consume an argument. |
 128
 129 ### Custom formatters
 130
 131   You can add custom formatters by extending the `debug.formatters` object. For example, if you wanted to add support for rendering a Buffer as hex with `%h`, you could do something like:
 132
 133 ```js
 134 const createDebug = require('debug')
 135 createDebug.formatters.h = (v) => {
 136   return v.toString('hex')
 137 }
 138
 139 // …elsewhere
 140 const debug = createDebug('foo')
 141 debug('this is hex: %h', new Buffer('hello world'))
 142 //   foo this is hex: 68656c6c6f20776f726c6421 +0ms
 143 ```
 144
 145 ## Browser support
 146   You can build a browser-ready script using [browserify](https://github.com/substack/node-browserify),
 147   or just use the [browserify-as-a-service](https://wzrd.in/) [build](https://wzrd.in/standalone/debug@latest),
 148   if you don't want to build it yourself.
 149
 150   Debug's enable state is currently persisted by `localStorage`.
 151   Consider the situation shown below where you have `worker:a` and `worker:b`,
 152   and wish to debug both. You can enable this using `localStorage.debug`:
 153
 154 ```js
 155 localStorage.debug = 'worker:*'
 156 ```
 157
 158 And then refresh the page.
 159
 160 ```js
 161 a = debug('worker:a');
 162 b = debug('worker:b');
 163
 164 setInterval(function(){
 165   a('doing some work');
 166 }, 1000);
 167
 168 setInterval(function(){
 169   b('doing some work');
 170 }, 1200);
 171 ```
 172
 173 #### Web Inspector Colors
 174
 175   Colors are also enabled on "Web Inspectors" that understand the `%c` formatting
 176   option. These are WebKit web inspectors, Firefox ([since version
 177   31](https://hacks.mozilla.org/2014/05/editable-box-model-multiple-selection-sublime-text-keys-much-more-firefox-developer-tools-episode-31/))
 178   and the Firebug plugin for Firefox (any version).
 179
 180   Colored output looks something like:
 181
 182   ![](https://cloud.githubusercontent.com/assets/71256/3139768/b98c5fd8-e8ef-11e3-862a-f7253b6f47c6.png)
 183
 184
 185 ## Output streams
 186
 187   By default `debug` will log to stderr, however this can be configured per-namespace by overriding the `log` method:
 188
 189 Example _stdout.js_:
 190
 191 ```js
 192 var debug = require('debug');
 193 var error = debug('app:error');
 194
 195 // by default stderr is used
 196 error('goes to stderr!');
 197
 198 var log = debug('app:log');
 199 // set this namespace to log via console.log
 200 log.log = console.log.bind(console); // don't forget to bind to console!
 201 log('goes to stdout');
 202 error('still goes to stderr!');
 203
 204 // set all output to go via console.info
 205 // overrides all per-namespace log settings
 206 debug.log = console.info.bind(console);
 207 error('now goes to stdout via console.info');
 208 log('still goes to stdout, but via console.info now');
 209 ```
 210
 211
 212 ## Authors
 213
 214  - TJ Holowaychuk
 215  - Nathan Rajlich
 216  - Andrew Rhyne
 217
 218 ## Backers
 219
 220 Support us with a monthly donation and help us continue our activities. [[Become a backer](https://opencollective.com/debug#backer)]
 221
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 252
 253
 254 ## Sponsors
 255
 256 Become a sponsor and get your logo on our README on Github with a link to your site. [[Become a sponsor](https://opencollective.com/debug#sponsor)]
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 288
 289 ## License
 290
 291 (The MIT License)
 292
 293 Copyright (c) 2014-2016 TJ Holowaychuk &lt;tj@vision-media.ca&gt;
 294
 295 Permission is hereby granted, free of charge, to any person obtaining
 296 a copy of this software and associated documentation files (the
 297 'Software'), to deal in the Software without restriction, including
 298 without limitation the rights to use, copy, modify, merge, publish,
 299 distribute, sublicense, and/or sell copies of the Software, and to
 300 permit persons to whom the Software is furnished to do so, subject to
 301 the following conditions:
 302
 303 The above copyright notice and this permission notice shall be
 304 included in all copies or substantial portions of the Software.
 305
 306 THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND,
 307 EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 308 MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 309 IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
 310 CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
 311 TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
 312 SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.