obtain the index of the selected item in select dropdownlist in javascript code example

Example 1: javascript get selected option

var e = document.getElementById("selectElementID");
var value=e.selectElement.options[e.selectedIndex].value;// get selected option value
var text=e.options[e.selectedIndex].text;//get the selected option text

Example 2: how to get the selected index of dropdown

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$('#ddlPartnerType option:selected').index()