Triggering reflow to toggle a CSS3 transition

My previous post on triggering reflow focused on forcing reflow to allow for transitions when an element is put into the DOM render tree. This post doesn’t present any new concepts, but provides an example of triggering reflow, in the same manner, to allow for applying style changes to a DOM element instantly and without a transition, then turning the transition back on.

The changes to an element are typically:

  • Turn off the transition on the element
  • Update some properties of the element (that are part of the transition), and force reflow so that the changes are applied instantly without transition
  • Turn on the transition again

In working with transitions, this scenario has come up frequently for me, as much as dealing with DOM elements being put into the render tree.

One classic example where this becomes necessary is in constructing a circular carousel, as the trick to make it circular is to make the first slide a copy of the last slide – so the carousel starts on the second slide and when you reach the last slide, the carousel instantly jumps to the first slide and slides over to the second slide. This is all invisible to the user, and it appears that the carousel has transitioned smoothly from the last slide to the first slide.

The code for a working circular carousel with 3 slides (plus a copy of the last slide) is presented below, with the classes for the different states of the slides being slide1pre (copy of slide 3), slide1, slide2, and slide3.

Note the point where it is necessary to trigger reflow in order to invisibly jump to the first slide.

.carousel-viewport { width:70px; height:70px; overflow:hidden; }
.carousel-container { width:1000px; }

.carousel-container.notransition { transition:transform 0s; }
.carousel-container.dotransition { transition:transform 0.5s; }

.carousel-container.slide1pre { transform:translateX(0px); }
.carousel-container.slide1 { transform:translateX(-70px); }
.carousel-container.slide2 { transform:translateX(-140px); }
.carousel-container.slide3 { transform:translateX(-210px); }

.test-block { width:50px; height:50px; float:left; margin:10px; color:#fff; background:#222; }
<p><a class="ia-start-color-change" href="#">Rotate carousel</a></p>

div class="carousel-viewport">
div class="ia-carousel-container carousel-container dotransition slide1">
div class="ia-slide-pre test-block">3</div>
div class="ia-slide-1 test-block">1</div>
div class="ia-slide-2 test-block">2</div>
div class="ia-slide-3 test-block">3</div>
var curSlide = 1; // start at slide1

$('.ia-start-color-change').click(function (event) {

var testBlockElem = $('.ia-carousel-container');

// slide 1 to slide 2
if (curSlide == 1) {

// slide 2 to slide 3
if (curSlide == 2) {

// slide 3 to slide1pre, then slide1pre to slide1
if (curSlide == 3) {

// turn off transition
// go to slide1pre invisibly and instantly (w/o transition)

// Force reflow to commit style changes to DOM
// allows us to re-apply transition rule, with the DOM updated to the carousel on slide1pre with no transition rule
testBlockElem[0].offsetWidth; // force reflow

// re-apply transition rule
// transition over to slide1

// reset slide counter
// (note subsequent increment in this function, so we'll be at curSlide=1 when this function finishes)
curSlide = 0;



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