JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" id="ordernumber" />
<select id="system">
    <option value="sys1">Sys1</option>
    <option value="sys2">Sys2</option>
</select>
<div id="Memo">Hi, I'm Memo</div>

CSS

#Memo {
    display: inline;
}

JavaScript

window.onload = function() {
    document.getElementById("ordernumber").addEventListener('keyup', takeawayfield, false);
    document.getElementById("system").addEventListener('change', takeawayfield, false);
    
    function takeawayfield()
    {   
        if (document.getElementById("system").value == "sys1") {
            toggleMemo(false);
        }
        else {
            toggleMemo(true);
        }
    }
        
    function toggleMemo(show) {
        var memo = document.getElementById("Memo");
        if (show) {
            memo.style.display = "inline";
        }
        else {
            memo.style.display = "none";
        }
    }
};