index.js

module.exports = rateLimit;

function rateLimit(limitCount, limitInterval, fn) {
  var fifo = [];

  // count starts at limit
  // each call of `fn` decrements the count
  // it is incremented after limitInterval
  var count = limitCount;

  function call_next(args) {
    setTimeout(function() {
      if (fifo.length > 0) {
        call_next();
      }
      else {
        count = count + 1;
      }
    }, limitInterval);

    var call_args = fifo.shift();

    // if there is no next item in the queue
    // and we were called with args, trigger function immediately
    if (!call_args && args) {
      fn.apply(args[0], args[1]);
      return;
    }

    fn.apply(call_args[0], call_args[1]);
  }

  return function rate_limited_function() {
    var ctx = this;
    var args = Array.prototype.slice.call(arguments);
    if (count <= 0) {
      fifo.push([ctx, args]);
      return;
    }

    count = count - 1;
    call_next([ctx, args]);
  };
}