Question: How can I check if textarea is hidden using javascript?

Answer: 
Did you try elm.getBoundingClientRect() ?

It will give all zero values if the element or a parent has display:none.  

With visibility:hidden the element is there and then has a boudning rectangle.

```
<html>
<head>
    <title>hidden</title>
</head>
<body>
<div style="display:none">
    <form>
        <textarea></textarea>
    </form>
</div>
<script>
  var rect = document.getElementsByTagName('TEXTAREA')[0].getBoundingClientRect();
  alert(rect.right === 0 ? 'hidden':'visible');
</script>
</body>
</html>

```
Wouldn't it be unhidden in the first place if your css isn't setting it to display: none; ?

If you want to hide it or show it you should just be able to use some JQuery:

```
$(document.body).css( "display", "none" );

```

or

```
$(myForm.elements).hide()

```

And so on.