How to Instantly Scroll to Position?

Question

How to instantly scroll window to some position with JavaScript, when smooth-scrolling is enabled?

:root {
    scroll-behavior: smooth;
}

Is there a way to ignore this CSS rule? Something like this:

window.scrollBy({ top: 0, behavior: 'instantly' });

Answer 1

Perhaps you could set the scroll-behavior before calling .scrollBy() and then reset it after.

var root = document.querySelector(':root');
var btnInstantScroll = document.querySelector('#btnInstantScroll');
var btnDefaultScroll = document.querySelector('#btnDefaultScroll');

btnInstantScroll.addEventListener('click', function() {

  // Change scroll behavior
  root.setAttribute("style", "scroll-behavior: auto;");

  // Timeout ensures styles are applied before scrolling
  setTimeout(function() {
    window.scrollBy(0, -2000);
    
    // Reset to CSS defaults.
    root.removeAttribute("style");
  }, 0)

})

btnDefaultScroll.addEventListener('click', function() {
  window.scrollBy(0, -2000);
})

:root {
  scroll-behavior: smooth;
}

.scrollable {
  height: 2000px;
  background: repeating-linear-gradient(#e66465, #e66465 20px, #9198e5 20px, #9198e5 25px);
}

.controls {
  padding: 15px;
  position: fixed;
  bottom: 0;
}

<div class="scrollable">

</div>

<div class="controls">
  <button type="button" id="btnInstantScroll">
    Instant scroll
  </button>

  <button type="button" id="btnDefaultScroll">
    Scroll using doc settings
  </button>
</div>