gistfile1.js

function throttle(fn, duration){
  var lastCall = new Date().getTime() // closure variable
    , timeout = null 

  duration = parseInt(duration, 10) // convert duration to int

  function throttled(){
    var currentCall = new Date().getTime() 
      , gap = currentCall - lastCall
      , self = this, args = arguments 
    
    if(timeout) { 
      window.clearTimeout(timeout)
      timeout = null
    }
    
    if(gap < duration) {
      timeout = window.setTimeout(function(){
        throttled.call(self, arguments)
      }, Math.max(throttle - gap, 0)) 
      // if gap < 0, timeout is equivalent to setImmediate
      return 
    }
    // otherwise call
    fn.call(self, args)
    // and set the last callTime to now (takes care of not using `currentCall`,
    // as fn.call can take time
    lastCall = new Date().getTime()
  }
  
  return throttled
}

gistfile2.js

/* Test */ 


var calls = []
  , throttleCalls = 0
  , normalCalls = 0
  , scroller = throttle(function(){
    throttleCalls++
    calls.push(new Date().getTime())
  }, 100)

window.addEventListener("scroll", scroller)
window.addEventListener("scroll", function(){
  normalCalls++
})


function getStats(){
  var r = [], l = calls.length
  for(;l--;) r[l] = calls[l] - (calls[l-1] || calls[l])
  return {
    throttleIntervals : r,
    normalCalls : normalCalls,
    throttleCalls : throttleCalls
  }
}

Throttle

Test output :

{
     "throttleIntervals":[
        0,
        128,
        100,
        101,
        102,
        103,
        109,
        121,
        114,
        101,
        100,
        100,
        1411,
        105,
        105,
        114,
        109,
        100,
        21363,
        126,
        118,
        104,
        107,
        101,
        100,
        103,
        101,
        100,
        100,
        119,
        111,
        116,
        118,
        120,
        120,
        129,
        101,
        117,
        100,
        101,
        100,
        109,
        125,
        118,
        116,
        100,
        131,
        101,
        100,
        105,
        102,
        128,
        122,
        121,
        121,
        102,
        122,
        114,
        139,
        113,
        101,
        100,
        109
     ],
     "normalCalls":153,
     "throttleCalls":63
  }