实现代码：
<select id=test11 size=5 style="width:50px"></select>
<select id="test" style="width:50px"></select>
<button onclick='test[test.length]=new Option("1","12");'>同时添加text和value</button>
<button onclick='test.insertBefore(document.createElement("option")).innerText="2";'>对text操作</button> <button onclick='test.appendChild(document.createElement("option")).setAttribute("value","3");'>对value操作</button>
<button onclick="alert(test.outerHTML)">view</button>
<button onclick="test.removeChild(test.children[0])">del1</button>
<button onclick="test.firstChild.removeNode()">del2</button>
<button onclick="test[0]=null">del3</button>
效果演示：
