Diagnostics
Diagnostics is a small debugging library which allows you to output your debug
logs by setting an environment variable. The library works for server-side and
client-size applications so it's great for writing isomorphic JavaScript.
The debug output can be triggered using environment variables on the server and
using localStorage, hashtags and window.name on the browser. If the debug output
is not enabled this module will result in an empty function causing the
JavaScript compiler engines to remove it completely from your code so there is
absolutely no performance overhead or excuses left to not use logging in your
code!
Installation
The module is released in the public npm registry and can easily be installed by
running.
npm install --save diagnostics
For client-side/front-end facing application we assume that you're using
browserify
as your build tool as the client code is bundled as the
browser.js
file in the root of this repository.
Usage
When you require the module it returns a function that expect a name or prefix
for the debug messages. This prefix is what you use to enable specific debug
messages.
The exported function of the module accepts 2 arguments:
name
The namespace of the debug logger.options
These options can only be applied to the server, not client code:
colors
: Enable or disable colors. Defaults to true if your stdout is a tty.stream
: The stream instance we should write our logs to. We default to
process.stdout
(unless you change the default using the .to
method).
var debug = require('diagnostics')('foo');
debug('hello world %d', 12);
In the example above you can see that we've created a new diagnostics function
called debug. It's name is set to foo
. So when we run this in Node.js using:
node index.js
We will see nothing in the console as the log messages are disabled by default.
But when set the DEBUG
or DIAGNOSTICS
environment variables to the name of
the debug function it will show up:
DIAGNOSTICS=foo node index.js
hello world 12
You can enable or disable specific diagnostic instances in the ENV variables by
separating them using a space or comma:
DEBUG=foo,-bar,primus:*
In the example above you also see an example of a wild card *
. This ensures
that anything after it or before it will be allowed.
To make it easier to see where the log messages are coming from they are
colored automatically based on the namespace you provide them. The deeper the
namespace, the lighter name will be toned as seen in the following output.
Browser
The usage for browser is exactly the same as for node. You require the
diagnostics
method and supply it with a name argument. The big difference is
that no longer can use environment variables as these only work on the server.
So to go around that you can use:
- hashtag The hashtag will be parsed using query string decoding. So if you
have an hash
#debug=foo
it will trigger all foo
lines to be dumped to your
browser console. - localStorage We will search for a query string in either the
env
or
debug
key of localStorage
. We again assume that the value has query string
encode value which contains either debug
or diagnostics
.
localStorage.env = 'diagnostics=foo'
. - window.name As
localStorage
is not available in all browsers, we provide
a fallback to window.name
which can contain the same values as the
localStorage
's env/debug keys.
Unlike the server, the output of the browser is not colored. The reason for this
that it would take a considerable amount of code. Which is not worth the benefit
as you usually want your front-end code to be as small as possible.
Multiple streams
Please note that this feature is server-side only as in the browser we can only
output to the console
The beauty of this logger is that it allows a custom stream where you can write
the data to. So you can just log it all to a separate server, database and what
not. But we don't just allow one stream we allow multiple streams so you might
want to log to disk AND just output it in your terminal. The only thing you need
to do is either use:
require('diagnostics').to([
stream1,
stream2
]);
To set multiple streams as the default streams or supply an array for the logger
it self:
var debug = require('diagnostics')('example', { stream: [
stream1,
stream2
]});
debug('foo');
License
MIT