我有选择框，并且选择的框选择了一个值，现在我可以更改值，我希望它应该选择更改的值而不是已经选择的值我像这样使用它var x= document.getElementById("numbervalue");
var y= document.getElementById("dayvalue");
ax = dnum.options[x.selectedIndex].value;
at = dDay.options[y.selectedIndex].value;上面只给我以前选择的值，而不是新的值
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呼啦一阵风
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<!DOCTYPE HTML>
<html>
<head>
<meta charset="utf-8">
<title>get value of select box</title>
<style>
body {
font-family: Courier, monospace;
}
#output {
margin-top:10px;
text-align:center;
padding:10px;
width: 200px;
height:100px;
border-style:groove;
}
.info {
font-size: 12px;
width: 270px;}
</style>
</head>
<body>
<h3>select box stack overflow</h3>
<p class = "info">On any change in an option element, the JS will use the vals from the numbervalue option element to reset the val in the dayvalue option element.<br><br>You must change the number to change anything</p>
<label for = "dayvalue">Choose a day:</label>
<select name="dayvalue" id="dayVal" onchange="readBoxes()">
<option value="m">Monday</option>
<option value="t">Tuesday</option>
<option value="w">Wednesday</option>
<option value="th">Thursday</option>
<option value="f">Friday</option>
<option value="sat">Saturday</option>
<option value="sun">Sunday</option>
</select>
<br>
<label for = "numbervalue">Choose a number:</label>
<select name="numbervalue" id="numVal" onchange="readBoxes()">
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
<option value="4">4</option>
<option value="5">5</option>
<option value="6">6</option>
<option value="7">7</option>
</select>
<div id="output">Day of Week</div>
<p>-h34dsp1nns</p>
<script>
function readBoxes() {
var out = document.getElementById("output");
var day = document.getElementById("dayVal");
var num = document.getElementById("numVal");
var numIndex = num.selectedIndex;
day.selectedIndex = numIndex; //resets the index
var dayVal = day[numIndex]; //gets the option element at an index
out.innerHTML = dayVal.text;
}
</script>
</body>
</html>
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