A bit of code that will limit the iteration of a function to a specific rate.

npm intall fnrate

-or-

npm install ben-bradley/fnrate

var fnrate = require('fnrate');

fnrate({
  rate: '10/sec',
  duration: '5 min', // will run for 5 minutes & stop
  times: 100, // `callback` will iterate 100 times
  max: 5, // [optional] there will only be 5 pending `callback`s at any time
  // `callback` will iterate for whichever is less: times or duration
  callback: function(next) {
    // do stuff
    next(); // next([error, [result]]);
  },
  done: function(err, results) {
    if (err) console.log(err);
    else console.log('all done!');
  }
});

var fnrate = require('fnrate');
var i = 0;

fnrate({
  rate: function () {
    if (i < 25) return '10/sec';
    else if (i < 50) return '20/sec';
    else if (i < 75) return '5/sec';
    else return '15/sec';
  },
  times: 100,
  max: 10,
  callback: function (next) {
    i += 1;
    console.log(i);
    next(null, i);
  },
  done: function (err, results) {
    console.log('all done!');
    done();
  }
});

• rate - The rate at which you wish to initiate your callback. Expects a string: n/period where n is a number and period is one of
  • 'sec'
  • 'second'
  • 'min'
  • 'minutes'
  • 'hr'
  • 'hour'
• duration - The length of time that you want the itaration to last. Expects a string: n period where n is the number of periods.
• times - The number of times that you want the callback to run.
• max - The maximum number of pending callbacks at any time.
• callback - The function to iterate. Provides a next function that must be called when complete to trigger the next iteration. If the next function is called with arguments, it will pass them through to the done;
• done - The function to call when the duration or times are complete.

I found that I wanted to be able to pause and resume the callbacks from within the callback so as of version 0.0.3, you can:

• options.max - Integer - Setting this option will cause fnrate to pause if there are ever more than this number of pending callbacks.
• pause() - Calling this.pause() within the callback will also pause the execution of other callbacks until this.resume() is called.
• resume() - Clears the pause() state and resumes execution of the callback.

npm test

-or-

mocha -R spec

• 0.0.5 - Made .rate able to accept a function to modify rates on the fly!
• 0.0.4 - Added code to catch race conditions
• 0.0.3 - More finely-tuned version of flow-control
• 0.0.2 - First atempt at flow-control
• 0.0.1 - Initial drop & npm publish