easuyui compbox中のonchange事件のきっかけ

class="easyui-combobox" name="site" style="width:300px;" id="problemType">
    <option value="3">   option>
    <option value="2">   option>
    <option value="4">    option>

$('#problemType').combobox({  
    onChange:function(newValue,oldValue){
        alert(newValue); 
    }  
});

$('#problemType').combobox('getValue');