SOURCE

function getOptions()
  {
  var x=document.getElementById("mySelect");
  var y="";
  for (i=0;i<x.length;i++)
    {
    y+=x.options[i].text;
    y+="<br />";
    }
  document.write(y);
  }

<form>
   请选择您喜欢的水果： 
  <select id="mySelect"> <option>苹果</option> <option>桃子</option> <option>香蕉</option> <option>桔子</option> </select> 
  <br>
  <br> 
  <input type="button" onclick="getOptions()" value="输出所有选项"> 
 </form>