Check if an element’s content is overflowing?

What’s the easiest way to detect if an element has been overflowed?

My use case is, I want to limit a certain content box to have a height of 300px. If the inner content is taller than that, I cut it off with an overflow. But if it is overflowed I want to show a ‘more’ button, but if not I don’t want to show that button.

Is there an easy way to detect overflow, or is there a better method?

Answer

If you want to show only an identifier for more content, then you can do this with pure CSS. I use pure scrolling shadows for this. The trick is the use of background-attachment: local;. Your css looks like this:

.scrollbox {
  overflow: auto;
  width: 200px;
  max-height: 200px;
  margin: 50px auto;

  background:
    /* Shadow covers */
    linear-gradient(white 30%, rgba(255,255,255,0)),
    linear-gradient(rgba(255,255,255,0), white 70%) 0 100%,
    
    /* Shadows */
    radial-gradient(50% 0, farthest-side, rgba(0,0,0,.2), rgba(0,0,0,0)),
    radial-gradient(50% 100%,farthest-side, rgba(0,0,0,.2), rgba(0,0,0,0)) 0 100%;
  background:
    /* Shadow covers */
    linear-gradient(white 30%, rgba(255,255,255,0)),
    linear-gradient(rgba(255,255,255,0), white 70%) 0 100%,
    
    /* Shadows */
    radial-gradient(farthest-side at 50% 0, rgba(0,0,0,.2), rgba(0,0,0,0)),
    radial-gradient(farthest-side at 50% 100%, rgba(0,0,0,.2), rgba(0,0,0,0)) 0 100%;
  background-repeat: no-repeat;
  background-color: white;
  background-size: 100% 40px, 100% 40px, 100% 14px, 100% 14px;
  
  /* Opera doesn't support this in the shorthand */
  background-attachment: local, local, scroll, scroll;
}

<div class="scrollbox">
  <ul>
    <li>Not enough content to scroll</li>
    <li>2</li>
    <li>3</li>
    <li>4</li>
    <li>5</li>
  </ul>
</div>


<div class="scrollbox">
  <ul>
    <li>Ah! Scroll below!</li>
    <li>2</li>
    <li>3</li>
    <li>4</li>
    <li>5</li>
    <li>6</li>
    <li>7</li>
    <li>8</li>
    <li>9</li>
    <li>10</li>
    <li>1</li>
    <li>2</li>
    <li>3</li>
    <li>4</li>
    <li>5</li>
    <li>6</li>
    <li>7</li>
    <li>8</li>
    <li>The end!</li>
    <li>No shadow there.</li>
  </ul>
</div>

The code and the example you can find on http://dabblet.com/gist/2462915

And an explanation you can find here: http://lea.verou.me/2012/04/background-attachment-local/.