Accurate Javascript setInterval replacement

interval.js

function interval(duration, fn){
  this.baseline = undefined
  
  this.run = function(){
    if(this.baseline === undefined){
      this.baseline = new Date().getTime()
    }
    fn()
    var end = new Date().getTime()
    this.baseline += duration
 
    var nextTick = duration - (end - this.baseline)
    if(nextTick<0){
      nextTick = 0
    }
    (function(i){
        i.timer = setTimeout(function(){
        i.run(end)
      }, nextTick)
    }(this))
  }

this.stop = function(){
   clearTimeout(this.timer)
 }
}

This code snippet can be used when a very accurate setInterval is needed. It will always be accurate ( 1+-ms in variance, but the mean will be the exact duration). Of course the function provided must run faster than the duration parameter. If for some reason the function takes more time than the duration in some occasions, the timer will still converge to the exact intervals very fast.

Example of use:

var timer = new interval(50, function(){
console.log(new Date().getTime())
})
timer.run()