extjs - Unable to dynamically change panel background image for IE, Chrome & Safari in extjs

Question

I have an EXTJS panel as desktop background. I have added some code to dynamically change the background image. In Firefox it is working well but it is not working in any of other browsers.

var panelbg = Ext.getCmp('windowarea').body;
var tree = Ext.getCmp('desktoptree');
if (tree.getSelectionModel().hasSelection()) 
{
    var selectedNode = tree.getSelectionModel().getSelection();
    var nodeid = selectedNode[0].data.id;
    var demo = "Data/wall/"+nodeid+".jpg";
    panelbg.setStyle('background-image','url('+demo+')');
    panelbg.setStyle('background-size','cover');
}

Please Help me.

Thanks in Advance