npm install debug-distA tiny node.js debugging utility modelled after node core's debugging technique.
Discussion around the V3 API is under way here
``bash`
$ npm install debug
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.
Example _app.js_:
`js
var debug = require('debug')('http')
, http = require('http')
, name = 'My App';
// fake app
debug('booting %s', name);
http.createServer(function(req, res){
debug(req.method + ' ' + req.url);
res.end('hello\n');
}).listen(3000, function(){
debug('listening');
});
// fake worker of some kind
require('./worker');
`
Example _worker.js_:
`js
var debug = require('debug')('worker');
setInterval(function(){
debug('doing some work');
}, 1000);
`
The __DEBUG__ environment variable is then used to enable these based on space or comma-delimited names. Here are some examples:
#### Windows note
On Windows the environment variable is set using the set command.
`cmd`
set DEBUG=*,-not_this
Note that PowerShell uses different syntax to set environment variables.
`cmd`
$env:DEBUG = "*,-not_this"
Then, run the program to be debugged as usual.
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 stdout is not a TTY, Date#toUTCString() is used, making it more useful for logging the debug information as shown below:
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:".
When running through Node.js, you can set a few environment variables that will
change the behavior of the debug logging:
| Name | Purpose |
|-----------|-------------------------------------------------|
| DEBUG | Enables/disabled specific debugging namespaces. |DEBUG_COLORS
| | Whether or not to use colors in the debug output. |DEBUG_DEPTH
| | Object inspection depth. |DEBUG_SHOW_HIDDEN
| | Shows hidden properties on inspected objects. |
__Note:__ The environment variables beginning with DEBUG_ end up being%o
converted into an Options object that gets used with /%O formatters.util.inspect()
See the Node.js documentation for
for the complete list.
Debug uses printf-style formatting. Below are the officially supported formatters:
| Formatter | Representation |
|-----------|----------------|
| %O | Pretty-print an Object on multiple lines. |%o
| | Pretty-print an Object all on a single line. |%s
| | String. |%d
| | Number (both integer and float). |%j
| | JSON. Replaced with the string '[Circular]' if the argument contains circular references. |%%
| | Single percent sign ('%'). This does not consume an argument. |
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:
`js
const createDebug = require('debug')
createDebug.formatters.h = (v) => {
return v.toString('hex')
}
// …elsewhere
const debug = createDebug('foo')
debug('this is hex: %h', new Buffer('hello world'))
// foo this is hex: 68656c6c6f20776f726c6421 +0ms
`
Debug's enable state is currently persisted by localStorage.worker:a
Consider the situation shown below where you have and worker:b,localStorage.debug
and wish to debug both. You can enable this using :
`js`
localStorage.debug = 'worker:*'
And then refresh the page.
`js
a = debug('worker:a');
b = debug('worker:b');
setInterval(function(){
a('doing some work');
}, 1000);
setInterval(function(){
b('doing some work');
}, 1200);
`
#### Web Inspector Colors
Colors are also enabled on "Web Inspectors" that understand the %c formatting
option. These are WebKit web inspectors, Firefox (since version
31)
and the Firebug plugin for Firefox (any version).
Colored output looks something like:
By default debug will log to stderr, however this can be configured per-namespace by overriding the log method:
Example _stdout.js_:
`js
var debug = require('debug');
var error = debug('app:error');
// by default stderr is used
error('goes to stderr!');
var log = debug('app:log');
// set this namespace to log via console.log
log.log = console.log.bind(console); // don't forget to bind to console!
log('goes to stdout');
error('still goes to stderr!');
// set all output to go via console.info
// overrides all per-namespace log settings
debug.log = console.info.bind(console);
error('now goes to stdout via console.info');
log('still goes to stdout, but via console.info now');
``
- TJ Holowaychuk
- Nathan Rajlich
- Andrew Rhyne
(The MIT License)
Copyright (c) 2014-2016 TJ Holowaychuk <tj@vision-media.ca>
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