Javascript extjs中组合框中的预选值

我想在ExtJS中实现以下组合框。问题是，如何在默认情况下选择第三个选项

<select name="meter_payment_option" onChange="smart_meter(this.value)"> 
    <option value="1">All Up-Front</option> 
    <option value="2">Reduced Up-Front</option> 
    <option value="3" selected="selected">No Up-Front</option> 
</select> 

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如何在默认情况下选择第三个选项（无前置）？

您需要将

值设置为默认值的id，例如：

<select name="meter_payment_option" onChange="smart_meter(this.value)"> 
    <option value="1">All Up-Front</option> 
    <option value="2">Reduced Up-Front</option> 
    <option value="3" selected="selected">No Up-Front</option> 
</select> 

var smart_meter_term = new Ext.form.ComboBox({
                  name:'smart_meter_term' ,
                  editable: false,
                  typeAhead: false, 
                  allowblank:false , 
                  triggerAction: 'all',
                  hiddenName: 'my_dropdown',
                  fieldLabel:'SmartM.T',
                  store:meter_payment_option_values,
                  displayField:'value',
                  valueField:'id',
                  mode:'local',
                  // default value is 3 (No Up-Front)
                  value: 3
                });