JSFiddle - React, Tailwind, and code Playground

HTML

<form id="loginform">
    <input type="text" name="email" id="email">
    <input type="password" name="password" id="password">
    <input type="submit" id="submit">
</form>

JavaScript

$(function(){    
    function validate(){
        if($('#email').val() !== '' && $('#password').val() !== '')
            $('#submit').prop('disabled', false);
        else
            $('#submit').prop('disabled', true);
    }

    // Validate after user input
    $('#email, #password').on('keyup change', validate);

    // Validate on mouse enter of body and login form
    // to catch auto-fills from roboform/1password etc...
    $('body, #loginform').on('mouseenter', validate);

    // Validate onload incase of autocomplete/autofill
    validate();
});