JSFiddle - React, Tailwind, and code Playground

HTML

FirstName:
<input id="fName" type="textbox" />Email:
<input id="f-email" type="textbox">
<button id="submit_btn" type="button" text="submit">Submit
    </>

JavaScript

$(document).ready(function () {
    $('#submit_btn').attr('disabled', 'disabled');
    var nameFlag = false;
    var emailFlag = false;
    var pwdFlag = false;
    $("#fName").focusout(function () {
        if ($(this).val() == '') {
            DisabledButton();
        } else if ($(this).val().length < 4) {
            DisabledButton();
        } else {
            EnabledButton();
        }
    });


    $('#f-email').focusout(function () {
        if ($(this).val() == '') {
            DisabledButton()
        } else if ($(this).val().length < 4) {
            DisabledButton();
        } else {
            EnabledButton();
        }
    });

    function EnabledButton() {
        $('#submit_btn').removeAttr('disabled');
    }

    function DisabledButton() {
        $('#submit_btn').attr('disabled', 'disabled')
    }
});