I want to get the width of an element in js and based on that width want to perform some animations. I am resizing the width of the below div from 1112px to 752px through CSS animation, when it reaches 752px I want animation on another element to begin.

<div id="mapId" class="map-root" lwc:dom="manual"></div>

.map-root {
    height: 370px;
    width: 1112px;
    border-radius: 5px;

.map-root-animation {
    animation: mapWidthAnimation 0.5s forwards 0s ease;

@keyframes mapWidthAnimation {
    0% {
        width: 1112px;
        height: 370px;

    100% {
        width: 752px;
        height: 370px;


On the click event of a button:

let mapWidth = this.template.querySelector('.map-root');
console.log(mapWidth.style.width);// I get blank value in the console.
if (mapWidth.style.width == 752px) { //do something }

1 Answer 1


The style attribute tells you what the style was set to. To get the actual current size, use getBoundingClientRect():


Note that this will be an actual number, not a string. For example, it'll be equal to 752, not 752px).

However, what you're probably looking for is to watch for the end of the animation:

mapWidth.addEventListener('animationend', this.handleAnimationEnd.bind(this));
  • Thanks again @sfdcfox
    – sumchans
    Apr 10, 2020 at 20:11
  • Thanks @sfdcfox ! getBoundingClientRect() is indeed the ticket. Thing is the querySelector result is quite inscrutable in debug because of the Proxy() that the aura_prod.js hides it behind. Is there some reference page which documents the members/methods that we can expect to "reach" through the Proxy which Aura imposes over the HTML elements? Dec 10, 2020 at 21:55
  • @BorisGaspic You can check the Locker API Viewer for methods and attributes you'll have access to.
    – sfdcfox
    Dec 10, 2020 at 21:58
  • @sfdcfox great reference, thank you for the link! I wasn't aware of that page Dec 12, 2020 at 16:13

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