html - Javascript onDrop attribute not assigned -

i encountered wierd problem in javascript. tried create div box in drop other divs. strangely ondrop-attribute doesn't assigned div allthough if read it, seems have it. error here? here's fiddle

    function creatleftrighttree(parentelement){             var lefttree = document.createelement("div");             var righttree = document.createelement("div");              lefttree.id="lefttree";             righttree.id="righttree";             lefttree.classname="dndcontainer";             righttree.classname="dndcontainer";               lefttree.ondrop="drop(event)";             righttree.ondrop="drop(event)";              righttree.ondragover="allowdrop(event)";              parentelement.appendchild(lefttree);             parentelement.appendchild(righttree);             righttree.innerhtml+= righttree.ondrop;             //it must not possible drop in left tree          }          function drop(ev) {         ev.preventdefault();         var data = ev.datatransfer.getdata("text");         var droptarget = ev.target;                 droptarget.appendchild(document.getelementbyid(data));         }  function allowdrop(ev) {             ev.preventdefault();         }  function drag(ev) {             ev.preventdefault();         } creatleftrighttree(document.getelementsbytagname("body")[0]); 

edit: updated fiddle , code less confusion. wrote alternativ function called drop(event). doesn't matter though, cause problem is: doesn't change ondrop-attribute

javascript event handlers all-lowercase; mean ondrop.

also, not assign strings; should assign function directly:

lefttree.ondrop = drop;