Required library edition:
Required library file: dhtmlxgrid.js

creates Editor object and switch selected cell to edit mode if allowed

<button onclick="(arguments[0]||window.event).cancelBubble=true; selectAndEdit()">Edit cell</button>
<script>
   function selectAndEdit(){
	mygrid.selectCell(rowIndex,cellIndex);
	mygrid.editCell();
   }
</script>

See also: editStop