Dead simpe pure JavaScript smooth scroll to top

scrolltotop.js

function scrollToTop () {
  var val = document.body.scrollTop || document.documentElement.scrollTop // THIS ONE IS HOW MUCH THE PAGE IS SCROLLED DOWN
  if (val > 1) { // if (val > 0) also works, BUT SINCE WE TAKE THE SQUARE ROOT OF THE VAL, WHEN THE VAL IS FLOAT, IT NEVERS REACHES TO ZERO (IN THIS CASE IT IS INTEGER)
    window.scrollBy(0, -Math.sqrt(val * 0.125) * 2) // HERE YOU CAN PLAY WITH THE VALUES TO CUSTOMIZE THE SPEED. 0.125 AFFECTS THE SMOOTHNESS, 2 AFFECTS THE OVERALL SPEED
    timeoutForScroll(true, 10) // OF COURSE YOU CAN CHANGE THE VALUE 10 TO CHANGE THE SPEED
  } else { // IF THE WINDOW IS ONLY 1 PIXELS AWAY FROM THE TOP
    windows.scrollBy(0, -1) // MAKE IT ZERO :D
    timeoutForScroll(false) // STOP THE TIMEOUT WITH OPERATOR
  }
}

function timeoutForScroll (operator, time) { //OPERATOR DECIDES WHAT TO DO, TIME AFFECTS SPEED (IN THIS EXAMPLE IT IS 10)
  var timeout // DECLARE THE TIMEOUT
  if (operator) { // IF TRUE SET THE TIMEOUT
    setTimeout( () => { scrollToTop() }, time ) // WHEN THE TIMEOUT ENDS CALL THE FUNCTION AGAIN
  } else {
    clearTimeout(timeout) // KILL THE TIMEOUT
  }
}