JSFiddle - React, Tailwind, and code Playground

HTML

<input type="email" name="email" placeholder="email" id="email"/>

JavaScript

var input = document.getElementById('email');

input.onblur = function() {
  var value = input.value
  
  if (value == "") {
    alert("empty");
  }

  if (value.indexOf("@") == -1) {
     alert("No @ symbol");
  }

}