Dynamic Debuglog

Let's say you're using util.debuglog to write debugging statements (like you should), and you wish you could hook in to process.env.NODE_DEBUG to dynamically turn them on and off without restarting your process. This allows you to do that.

Maybe you have a repl available in your app, or you open a route, or maybe you want to trigger it programmatically. If you can set a variable on the process.env object, you can turn your debugging statements on and off.

Performance Notes

In order to be dynamic, this debugger must check process.env.NODE_DEBUG on each debug statement. When in debug mode, this additional check is totally negligible. But when not debugging, it still must perform the check. This is much slower than the empty function that core util.debuglog calls when not in debug mode.

No problem! When you instantiate a dynamic debug logger, it will make a one-time check at process.env.NODE_ENV, so it can be parameterized to revert to the static core version of util.debuglog in certain environments. You can be dynamic in development and you can sacrifice flexibility for speed in production - with no change in code. (See stingy mode below for how this works.)

See below for benchmarks. You may choose to go dynamic all the way.

API: Comparison with util.debuglog

ddbuglog is designed to be used exactly like you use util.debuglog.

var coreDebug = require('util').debuglog('neatstuff');
var dynamicDebug = require('ddebuglog')('neatstuff');

coreDebug('This statement never prints.');
dynamicDebug('This statement never prints.');

process.env.NODE_DEBUG = 'neatstuff';

coreDebug('This statement still never prints');
dynamicDebug('But this one prints, because NODE_DEBUG is now %s', process.env.NODE_DEBUG);

// prints to stderr:
// NEATSTUFF 4918: But this one prints, because NODE_DEBUG is now neatstuff

Stingy mode

Can't afford the milliseconds? Youf can choose to revert to core util.debug in certain environments. Pass in an object with a useStatic attribute for the second argument:

// process.env.NODE_DEBUG not set to 'neatstuff'
var flexibleDebugger = dynamicDebug('neatstuff', {useStatic: 'production'});

process.env.NODE_DEBUG = 'neatstuff';

debug('This will still not print if process.env.NODE_ENV is `production`');

useStatic can be an Array of strings or a single string. If present when creating a ddebuglog, it will revert to the static core module when process.env.NODE_ENV matches. Simple enough, right?

Benchmarks

Using benchmark.js on a MacBook Air 2.2GHz i7 with 8GB RAM, here is a comparison of Node core util.debuglog and ddebuglog. As you can see, running in stingy mode is exactly the same as core (because that's all it is.

If you want to stay dynamic all the way, you can pass over 1500 non-active debug statements and stilladd only 1ms of latency.

[Baseline] Running an empty function x 96,610,538 ops/sec ±0.97% (94 runs sampled)
[Non-debug mode] Dynamic debuglog x 1,499,211 ops/sec ±0.99% (93 runs sampled)
[Non-debug mode] Node core debuglog x 97,839,585 ops/sec ±0.76% (94 runs sampled)
[Non-debug mode] Dynamic debuglog with active useStatic x 96,241,918 ops/sec ±1.91% (92 runs sampled)

[Debug mode] Dynamic debuglog x 160,839 ops/sec ±1.33% (91 runs sampled)
[Debug mode] Node core debuglog x 165,748 ops/sec ±1.28% (92 runs sampled)

Test

npm test to see it in action.

License

MIT

Hopes

You find it useful. :)