Javascript Update Attribute

   <input type="text" name="araButon" onKeyUp="return arama()" class="form-control filter" data-filter="app" id="focusedInput"/>

I want to update 'data-filter' value by javascript

I tryed this code :

var gelenText = document.getElementById("focusedInput"); //document.getElementById("focusedInput").getAttribute("data-filter")=gelenText;

Can someone help me?

Thanks...