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() == "")
    	firstName.addClass("errorInput");
     else
     firstName.removeClass("errorInput")
      
      if(lastName.val() == "")
    	lastName.addClass("errorInput");
     else
    	 lastName.removeClass("errorInput")

    });