JSFiddle - React, Tailwind, and code Playground

HTML

<select size="6" name="operator" id="operator" size="5" multiple="">
    <option value="1" >One</option>
    <option value="2" >Two</option>
    <option value="10" >Ten</option>
</select>

<input type="button" id="get" value="Get selected items" />

JavaScript

$('#get').click(function(){
    $("#operator").find('option:selected').each(function(){
        alert(this.value);
    });
});