selectedIndex

function displayResult(){
    var x=document.getElementById("mySelect").selectedIndex;
    var y=document.getElementById("mySelect").options;
    alert("索引: " + y[x].index + " is " + y[x].text);
}
</script>
</head>
<body>

<form>
选择你最喜欢的水果:
<select id="mySelect">
    <option>Apple</option>
    <option>Orange</option>
    <option>Pineapple</option>
    <option>Banana</option>
</select>
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原文地址：https://www.cnblogs.com/huangxingyuan/p/6395710.html