Flexbox height not updating when content changes

This works for me:

var elem = document.getElementById("myFlexbox");elem.style.display='none';elem.offsetHeight; // no need to store this anywhere, the reference is enoughelem.style.display='flex';

Also see: How can I force WebKit to redraw/repaint to propagate style changes?

In order to work in Chrome, it needs a refresh or some kind of reflow. DEMO

If you script force the main container to be recalculated, you have something that works.(this looks like some very old bug of Opera)

In order to do that, we can switch from position static to relative and use a pseudo to insert some content.

CLASS wrapper becomes an ID to easily select it via JavaScript

<div id="wrapper">    <div class="column1">This column Has some content</div>    <div class="column2">This column also has some content        <div id="contentToHide">            <p>Sed egestas, ante et vulputate volutpat, eros pede semper est, vitae luctus metus libero eu augue. Morbi purus libero, faucibus adipiscing, commodo quis, gravida id, est. Sed lectus. Praesent elementum hendrerit tortor. Sed semper lorem at felis. Vestibulum volutpat, lacus a ultrices sagittis, mi neque euismod dui, eu pulvinar nunc sapien ornare nisl. Phasellus pede arcu, dapibus eu, fermentum et, dapibus sed, urna.</p>        </div>    </div></div><button id="removeButton">Remove Content</button><br/><button id="addButton">Add Content</button>

javaScript update

document.getElementById('removeButton').addEventListener("click", function (event) {    document.getElementById('contentToHide').classList.add("hidden");    document.getElementById('wrapper').classList.add("prelative");});document.getElementById('addButton').addEventListener("click", function (event) {    document.getElementById('contentToHide').classList.remove("hidden");    document.getElementById('wrapper').classList.remove("prelative");});

CSS update:

#wrapper {    display: flex;    width: 400px;    margin-bottom: 30px;}.column1 {    padding: 10px;    background: #DDD;}.column2 {    padding: 10px;    background: #EEE;    width:50%;}#contentToHide.hidden {    display: none;}.prelative {    position:relative;}div:before {    content:attr(class);    left:-9999px;    position:absolute;}

Actually, for .hidden and pseudo you can just do :

#contentToHide.hidden ,div:before {    content:attr(class);    left:-9999px;    position:absolute;}

Try to set height: 100% for columns