derf

derf

debug. perf. derf?

Simple wrappers for debugging function performance.

• based on the debug module
• handles most common function patterns
• no performance hit in production

Example

Wrap Functions

// DEBUG=sync:* node script.js
import * as derf from 'derf';

const fn = derf.sync('sync:fn', function(a, b) {
  // slow operation
  return value;
});

Wrap Async Functions

// DEBUG=async:* node script.js
import * as derf from 'derf';

const fn1 = derf.callback('async:fn1', function(foo, bar, cb) {
  // slow operation
  callback(null, value);
});

const fn2 = derf.promise('async:fn2', function(foo, bar) {
  // slow operation
  return Promise.resolve(value);
});

Wrap Express Middleware

// DEBUG=middleware:* node script.js
import * as derf from 'derf';

const fn1 = derf.middleware('middleware:fn1', function(req, res, next) {
  // slow operation
  res.send('foo');
});

const fn2 = derf.middleware('middleware:fn2', function(req, res, next) {
  // slow operation
  next();
});

const fn3 = derf.middleware('middleware:fn3', function(err, req, res, next) {
  // slow operation
  request('/something').pipe(res);
});

API

Every function wrapper takes in the following arguments:

• namespace - Required. A string to pass to debug or a debug function.
• fn - Required. A function to wrap.
• printer - Optional. A function to customize what is logged.

derf.sync(namespace, fn, [printer])

Wraps a synchronous function.

derf.callback(namespace, fn, [printer])

Wraps a node-style async function. derf will intercept the last function passed in. Meaning it can work with the following types of argument orders.

const fn1 = derf.callback('namespace1', function(a, b, callback) { });

const fn2 = derf.callback('namespace1', function(a, callback, b) { });

const fn1 = derf.callback('namespace1', function(callback, a, b) { });

derf.promise(namespace, fn, [printer])

Wraps a function that returns a promise.

derf.middleware(namespace, fn, [printer])

Wraps express middleware, route handlers, and error handlers.

Custom Logging

You can pass in a function as the last argument of each derf wrapper to customize what is logged. The function must return a string and is passed the following arguments:

• debug - function. the debug instance.
• time - number. the time in nanoseconds array. the function to to run.
• args - array. the arguments the function was called with.
• retArgs - array. the error/value the function was resolved with.

For example, a simple printer could look like this:

function simplePrinter(debug, time, callArgs, retArgs) {
  const [err, res] = retArgs; // not available for middleware

  if (err) {
    debug('failed in %s nanoseconds', time);
  } else {
    debug('finished in %s nanoseconds', time);
  }
}

Caveats

TODO