JSFiddle - React, Tailwind, and code Playground

by eget teteete

HTML

<form name[myForm] action="#" onsubmit="return validateForm()">
  <input type="text" class="text" placeholder='Первое' name="fname"> <br>
  <button type="submit" class="send-btn"> Отправить</button>
  <p class="send-mssg">Отплавлено</p>
  
</form>

CSS

form{
  margin: 0 auto;
  border: 1px solid green;
  padding: 5px;
}
.send-mssg{
  display: none;
}

JavaScript

function validateForm() {
	let send = documet.getElementByClassName('send-btn'),
  	sendMs = documet.getElementByClassName('send-mssg');
    let x = document.forms["myForm"]["fname"].value;
    if (x == "") {
        alert("Ваше сообщение не от");
        return false;
    } else{
    	send.addEventListener('click', function(){
      	sendMs.style.display = block;
      })
    }
}