200 lines
6.6 KiB
Markdown
200 lines
6.6 KiB
Markdown
# debug
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tiny node.js debugging utility modelled after node core's debugging technique.
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## Installation
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```bash
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$ npm install debug
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```
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## Usage
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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.
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Example _app.js_:
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```js
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var debug = require('debug')('http')
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, http = require('http')
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, name = 'My App';
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// fake app
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debug('booting %s', name);
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http.createServer(function(req, res){
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debug(req.method + ' ' + req.url);
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res.end('hello\n');
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}).listen(3000, function(){
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debug('listening');
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});
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// fake worker of some kind
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require('./worker');
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```
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Example _worker.js_:
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```js
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var debug = require('debug')('worker');
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setInterval(function(){
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debug('doing some work');
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}, 1000);
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```
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The __DEBUG__ environment variable is then used to enable these based on space or comma-delimited names. Here are some examples:
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#### Windows note
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On Windows the environment variable is set using the `set` command.
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```cmd
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set DEBUG=*,-not_this
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```
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Note that PowerShell using different syntax to set environment variables.
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```cmd
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$env:DEBUG = "*,-not_this"
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```
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Then, run the program to be debugged as usual.
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## Millisecond diff
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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.
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When stdout is not a TTY, `Date#toUTCString()` is used, making it more useful for logging the debug information as shown below:
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## Conventions
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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".
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## Wildcards
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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=*`.
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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:".
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## Browser support
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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`:
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```js
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localStorage.debug = 'worker:*'
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```
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And then refresh the page.
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```js
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a = debug('worker:a');
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b = debug('worker:b');
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setInterval(function(){
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a('doing some work');
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}, 1000);
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setInterval(function(){
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b('doing some work');
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}, 1200);
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```
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#### Web Inspector Colors
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Colors are also enabled on "Web Inspectors" that understand the `%c` formatting
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option. These are WebKit web inspectors, Firefox ([since version
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31](https://hacks.mozilla.org/2014/05/editable-box-model-multiple-selection-sublime-text-keys-much-more-firefox-developer-tools-episode-31/))
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and the Firebug plugin for Firefox (any version).
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Colored output looks something like:
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## Output streams
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### stderr vs stdout
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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).
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You can also set an alternative logging method per-namespace by overriding the `log` method on a per-namespace or globally:
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Example _stdout.js_:
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```js
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var debug = require('debug');
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var error = debug('app:error');
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// by default stderr is used
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error('goes to stderr!');
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var log = debug('app:log');
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// set this namespace to log via console.log
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log.log = console.log.bind(console); // don't forget to bind to console!
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log('goes to stdout');
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error('still goes to stderr!');
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// set all output to go via console.info
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// overrides all per-namespace log settings
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debug.log = console.info.bind(console);
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error('now goes to stdout via console.info');
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log('still goes to stdout, but via console.info now');
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```
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### Save debug output to a file
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You can save all debug statements to a file by piping them.
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Example:
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```bash
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$ DEBUG_FD=3 node your-app.js 3> whatever.log
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```
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### Terminal colors
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By default colors will only be used in a TTY. However this can be overridden by setting the environment variable `DEBUG_COLORS` to `1`.
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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`.
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## Authors
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- TJ Holowaychuk
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- Nathan Rajlich
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- Andrew Rhyne
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## License
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(The MIT License)
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Copyright (c) 2014-2016 TJ Holowaychuk <tj@vision-media.ca>
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Permission is hereby granted, free of charge, to any person obtaining
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a copy of this software and associated documentation files (the
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'Software'), to deal in the Software without restriction, including
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without limitation the rights to use, copy, modify, merge, publish,
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distribute, sublicense, and/or sell copies of the Software, and to
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permit persons to whom the Software is furnished to do so, subject to
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the following conditions:
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The above copyright notice and this permission notice shall be
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included in all copies or substantial portions of the Software.
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THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND,
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EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
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IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
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CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
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TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
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SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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