js向html中的下拉框赋值

javascript方法：

for(var i=0;i<operTypes.length;i++){  

   var tOption= document.createElement("Option");
        tOption.text = operTypes[i];
        tOption.selected = false;
        tOption.value = operTypes[i];
      document.getElementById("Oper_Type").options.add(tOption); 

   }

html下拉框

<select name="Oper_Type" id="Oper_Type">
          <option selected="selected" value="">请选择</option>
          </select>