tiny node.js debugging utility modelled after node core's debugging technique.
$ npm install debug
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.
var debug = require('debug')('http')
, http = require('http')
, name = 'My App';
// fake app
debug('booting %s', name);
debug(req.method + ' ' + req.url);
// fake worker of some kind
var debug = require('debug')('worker');
debug('doing some work');
The __DEBUG__ environment variable is then used to enable these based on space or comma-delimited names. Here are some examples:
![debug http and worker](http://f.cl.ly/items/18471z1H402O24072r1J/Screenshot.png)
## Millisecond diff
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.
When stderr is not a TTY, `Date#toUTCString()` is used, making it more useful for logging the debug information as shown below:
_(NOTE: Debug now uses stderr instead of stdout, so the correct shell command for this example is actually `DEBUG=* node example/worker 2> out &`)_
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".
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=*`.
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:".
## Browser support
Debug works in the browser as well, currently persisted by `localStorage`. For example if you have `worker:a` and `worker:b` as shown below, and wish to debug both type `debug.enable('worker:*')` in the console and refresh the page, this will remain until you disable with `debug.disable()`.
a = debug('worker:a');
b = debug('worker:b');
a('doing some work');
a('doing some work');
(The MIT License)
Copyright (c) 2011 TJ Holowaychuk <[email protected]>
Permission is hereby granted, free of charge, to any person obtaining
a copy of this software and associated documentation files (the
'Software'), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:
The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.
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TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.