<script>
function notice(i)
{
if(i==2)
{window.alert("hello");}
}
</script>
<select onchange="notice(2)">
<option >1</option>
<option >2</option>
function notice(i)
{
if(i==2)
{window.alert("hello");}
}
</script>
<select onchange="notice(2)">
<option >1</option>
<option >2</option>
onchange是要改变选择项才会触发的