Get the selected value of the select tag
1.1 Example explanation
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Examples</title>
</head>
<body>
<select name="testSelect" id="testSelect">
<option value="1">1</option>
<option value="2">2</option>
<!-- selected="selected" specifies that the option (when first displayed in the list) appears selected. -->
<option value="3" selected="selected">3</option>
<option value="4">4</option>
<option value="5">5</option>
</select>
<!--[if !IE]><!-->
<script src="http://cdn.bootcss.com/jquery/3.2.1/jquery.min.js"></script>
<!--<![endif]-->
<!--[if lte IE 9]>
<script src="https://cdn.bootcss.com/jquery/1.8.3/jquery.min.js"></script>
<![endif]-->
<script>
//Js gets the selected value of the select tag
var obj = document.getElementById("testSelect");
var index = obj.selectedIndex; //selected index
var text = obj.options[index].text; //select text
var val = obj.options[index].value; //selected value
//Get the selected select value in jQuery
var text=$('#testSelect option:selected').text(); //selected text
var val=$('#testSelect option:selected') .val(); //selected value
var index=$("#testSelect").get(0).selectedIndex; //索引
</script>
</body>
</html>