JSFiddle - React, Tailwind, and code Playground

HTML

<form name="temperature_form" action="">
    Convert Celsius to Fahrenheit:<br>
    <input type="text" name="converterCtoF" id="converterCtoF"><br>
    <input type="submit" value="Submit">
</form>

JavaScript

document.forms["temperature_form"].onsubmit = function(){
    var c = document.getElementById("converterCtoF").value;
    var f = (9/5)*c+32;
    alert(f);
    return false;
}