how to revert position of a jquery UI draggable based on condition

Question

I have an element which is draggable and an element which is droppable. Once the dragged item is dropped on the dropzone I am trying to execute the following jquery psuedo c

Answer 1

There are some built-in options for this, on your .draggable(), set the revert option to 'invalid', and it'll go back if it wasn't successfully dropped onto a droppable, like this:

$("#draggable").draggable({ revert: 'invalid' });

Then in your .droppable() set what's valid for a drop using the accept option, for example:

$("#droppable").droppable({ accept: '#draggable' });​

Anything not matching this selector gets reset when you let go, you can see a full demo here. The accept option also takes a function if you need filtering a selector can't provide, like this:

$("#droppable").droppable({ 
  accept: function(dropElem) {
    //dropElem was the dropped element, return true or false to accept/refuse it
  }
});​