JSFiddle - React, Tailwind, and code Playground

HTML

<select name="form" id="aForm">
        <option value="a">choice1</option>
        <option value="b">choice2</option>
        <option value="c">choice3</option>
     </select>

     <input type="text" style="width:285px" name="textField" id="textField"/>

JavaScript

function hideShowTF(s) { 
    if ($(s).val() == "a") $("#textField").hide();
    else $("#textField").show();
}

$("#aForm").on("change", function() {hideShowTF(this);});

hideShowTF("#aForm");