CSS3 Transition: Slideup Box (Take 2)

Demo and source code

This post is to propose a better solution for creating an expandable/slideup box. My previous implementation has a flaw -- the fixed "max-height" truncate part of the content when its height grows. This solution will resolve this issue.

First, we have the following markup.

<article>
  <h2>Click me to expand</h2>
  <div class="content_w">
    <div class="content">
      Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do 
      eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut 
      enim ad minim veniam, quis nostrud exercitation ullamco laboris 
      nisi ut aliquip ex ea commodo consequat...
    </div>
  </div>
</article>

When users click inside an <article>, the content area will slide down (expand) or slide up (collapse). The title (<h2>) will always be visible.

The idea is to wrap the content inside a wrapper (div.content_w). The wrapper will hide any overflown content. We will change the height of the wrapper to create a slide up/down effect.

article .content_w {
  overflow: hidden;
  height: 0;
}
article .content_w.transition {
  -webkit-transition: height 0.5s;
     -moz-transition: height 0.5s;
       -o-transition: height 0.5s;
          transition: height 0.5s;
}

The wrapper needs to have "overflow: hidden" in order to clip the overflown content. We set "height: 0" to collapse the box initially.

The transition will take effect on the wrapper's height. When the box needs to be collapsed, we set the wrapper's height to 0. CSS3 transition will smoothly slide up the box. When expanding (sliding down), we set the wrapper's height back to the height of its enclosed content.

$('article').on('click', function() {
  slide($('.content', this)); 
});

function slide(content) {
  var wrapper = content.parent();
  var contentHeight = content.outerHeight(true);
  var wrapperHeight = wrapper.height();

  wrapper.toggleClass('open');
  if (wrapper.hasClass('open')) {
    setTimeout(function() {
      wrapper.addClass('transition').css('height', contentHeight);
    }, 10);
  }
  else {
    setTimeout(function() {
      wrapper.css('height', wrapperHeight);
      setTimeout(function() {
        wrapper.addClass('transition').css('height', 0);
      }, 10);
    }, 10);
  }

  wrapper.one('transitionEnd webkitTransitionEnd transitionend oTransitionEnd msTransitionEnd', function() {
    if(wrapper.hasClass('open')) {
      wrapper.removeClass('transition').css('height', 'auto');
    }
  });
}

The trick is that we don't want to keep a fixed height on the wrapper when it finishes expanding. A fixed height will clip its content when it grows, or leave unnecessary space at the bottom when the content shrinks. To fix that, we need to set height back to "auto" in order to "relax" the height. However, setting "height: auto" on HTML elements with CSS3 transition will make the transition have no effect. We have to remove transitions before setting "height: auto".

Demo and source code

Tested in Chrome, Safari, FireFox, and Opera Mobile Emulator