How to make extjs grid selectable

Ext.core.Element.prototype.unselectable = function() {
            var me = this;
            if (me.dom.className.match(/(x-grid-table|x-grid-view)/)) {
                return me;
            }
            me.dom.unselectable = "on";
            me.swallowEvent("selectstart", true);
            me.applyStyles("-moz-user-select:none;-khtml-user-select:none;");
            me.addCls(Ext.baseCSSPrefix + 'unselectable');
            return me;
        };

I copied the code from http://kevin.chibaole.com/135