Loop Javascript (or Actionscript!) array based on index

Looping arrays is particularly useful for things like photo galleries and other iterative processes where you want the "next photo" button on a gallery to continue from the beginning of the album after the user passes the last photo.

In my humble opinion, I believe this functionality should be built into the core of Ecmascript ( For example, something like myArray[-2] should really return the second last element in the array) but alas we have to write it ourselves, so here goes...

//loop array indexes & return the specified element:
function getElement(index,fromArray){
    while( index>fromArray.length-1 ){ index -= (fromArray.length);}
    while( index<0 ){ index = (fromArray.length)+index }
    return(fromArray[index])
}

//EXAMPLE:
var a = ['a1','b2','c3','d4','e5'] //create a simple 5 element array

alert(getElement(6,a)) //alerts 'b2'
alert(getElement(-2,a)) //alerts 'd4'