JSFiddle - React, Tailwind, and code Playground

HTML

<select id="selectBox" name="select" size="15" style="width:190px;">  
    <option value="1">1</option>
    <option value="2">2</option>
    <option value="3">3</option>
    <option value="4">4</option>
    <option value="5">5</option>
</select>

JavaScript

var selectbox = document.getElementById("selectBox");

var x = [];

function calculate()
    {
        for (var i = 0; i < selectbox.options.length; i++)
        {
            x[i]=selectbox.options[i].value;
            alert=(x[i]);
        }

    }
calculate();