HTMLSelectElement: selectedIndex property
The selectedIndex property of the HTMLSelectElement interface is the numeric index of the first selected <option> element in a <select> element, if any, or −1 if no <option> is selected. Setting this property selects the option at that index and deselects all other options, while setting it to -1 deselects any currently selected options.
Value
A number.
Examples
HTML
html
<p id="p">selectedIndex: 0</p>
<select id="select">
<option selected>Option A</option>
<option>Option B</option>
<option>Option C</option>
<option>Option D</option>
<option>Option E</option>
</select>
JavaScript
js
const selectElem = document.getElementById("select");
const pElem = document.getElementById("p");
// When a new <option> is selected
selectElem.addEventListener("change", () => {
const index = selectElem.selectedIndex;
// Add that data to the <p>
pElem.textContent = `selectedIndex: ${index}`;
});