JSFiddle - React, Tailwind, and code Playground

HTML

<form method=post>
    <input type="text" id='first_name'>
    <input type="text" id='second_name'>
    <input type="submit" value="Submit" id="submit" disabled>
</form>

JavaScript

$(':text').keyup(function() {
    if($('#first_name').val() != "" && $('#second_name').val() != "") {
       $('#submit').removeAttr('disabled');
    } else {
       $('#submit').attr('disabled', true);   
    }
});