Extjs 确认框

Ext.MessageBox.show({
title:'${uiLabelMap.certainOperation}',
msg:'是否要执行此操作？',
buttons:{yes:'确认',cancel:'取消'},
icon:Ext.MessageBox.QUESTION,
fn:function(btn, text) {
    if(btn=='yes') {
        alert("YES");
    }
}
});