Resize event for textarea?

Chrome doesn’t capture the resize event and that Chrome doesn’t capture the mousedown, so you need to set the init state and then handle changes through mouseup:

jQuery(document).ready(function(){
   var $textareas = jQuery('textarea');

   // store init (default) state   
   $textareas.data('x', $textareas.outerWidth());
   $textareas.data('y', $textareas.outerHeight()); 

   $textareas.mouseup(function(){

      var $this = jQuery(this);

      if (  $this.outerWidth()  != $this.data('x') 
         || $this.outerHeight() != $this.data('y') )
      {
          // Resize Action Here
          alert( $this.outerWidth()  + ' - ' + $this.data('x') + '\n' 
               + $this.outerHeight() + ' - ' + $this.data('y')
               );
      }
  
      // store new height/width
      $this.data('x', $this.outerWidth());
      $this.data('y', $this.outerHeight()); 
   });

});

HTML

<textarea></textarea>
<textarea></textarea>

You can test on JSFiddle

Note:

1. You could attach your own resizable as Hussein has done, but if you want the original one, you can use the above code
2. As Bryan Downing mentions, this works when you mouseup while your mouse is on top of a textarea; however, there are instances where that might not happen like when a browser is not maximized and you continue to drag beyond the scope of the browser, or use resize:vertical to lock movement.

For something more advanced you’d need to add other listeners, possibly a queue and interval scanners; or to use mousemove, as I believe jQuery resizable does — the question then becomes how much do you value performance vs polish?

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Update: There’s since been a change to Browsers’ UI. Now double-clicking the corner may contract the textbox to its default size. So you also may need to capture changes before/after this event as well.