JSFiddle - React, Tailwind, and code Playground

HTML

<input id="firstName" type="text" />
<input id="lastName" type="text" />
<a href="#" id="button">SEND</a>

CSS

.errorInput{
  border-color:red;
}

JavaScript

var firstName = $("#firstName");
var lastName = $("#lastName");

$('#button').click(function () {
		if(firstName.val() === "" || lastName.val() === ""){
			firstName.addClass("errorInput");
			lastName.addClass("errorInput");
		} else {
    	firstName.removeClass("errorInput");
			lastName.removeClass("errorInput");
    }
    
    if ($(":input").hasClass("errorInput")) {
			alert("false");
		} else {
			alert("true");
		}
 });