JSFiddle - React, Tailwind, and code Playground

HTML

<FORM NAME="myform" ACTION="" METHOD="GET">Age: <BR>
<INPUT TYPE="text" NAME="age" VALUE=""><P>
<INPUT TYPE="button" NAME="button" Value="Click" onClick="checkMyAge(form)">
</FORM>

JavaScript

function checkMyAge(form) {
    var age = form.age.value;
    if (age >= 21) {
        alert("Over 21! Age tested:" + age);
    }
    else {
        alert("Under 21! Age tested:" + age);
    }
}