console 命令行工具 X clear

console

function disable()
  {
  document.getElementById("mySelect").disabled=true
  }
function enable()
  {
  document.getElementById("mySelect").disabled=false
  }

<form> 
  <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="disable()" value="禁用列表"> 
  <input type="button" onclick="enable()" value="启用列表"> 
 </form>