常见简单功能

<select id="slec">
<option>请选择</option>
<option>1</option>
<option>2</option>
<option>3</option>
<option>4</option>
</select>

<script type="text/javascript">
var oslec=document.getElementById("slec");
var olen=oslec.options.length;
oslec.options[2].innerHTML="哈哈";
oslec.onchange=function(){
var index=oslec.selectedIndex;
var otext=oslec.options[index].text;
console.log(otext)
}
</script>