JSFiddle - React, Tailwind, and code Playground

HTML

<select onchange="javascript:get_api_key(this.value);" name="service">

<option value="">Select your Service</option>
<optgroup label="Apple Iphone">
<option value="53">Apple </option>
<option value="72">Ipad </option>
<option value="77">iPhone</option>
<option value="24">Iphone</option>
</optgroup>
</select>

JavaScript

function get_api_key(this) {
    alert(this.value);
    }