用HTML创建/显示欢迎消息

Question

我正在尝试在用户提交电子邮件后显示欢迎消息，但是在第一次提交后，我的味精开始随机显示。如何解决这个问题。

function emailVerification() {

  var emailContato = document.getElementById("emailForm").value;

  if (emailContato.trim() == "") {
    alert("Email inválido!");
  } else {

    alert('Email cadastrado com sucesso!');
    document.getElementById("teste").innerHTML = "Seja bem vindo" + " " + emailContato + "!";
    document.getElementById("boas-vindas").style.visibility = "visible";

    const event = document.addEventListener("click", function(e) {
      e.preventDefault();
    });

  }
}

#boas-vindas {
  visibility: hidden;
  color: #121;
  font-size: medium;
  font-family: "Georgia", Times, 'Times New Roman', serif;
}

<div id="boas-vindas">
  <label id="teste">Mensagem</label>
</div>

<div>      
  <input type="email" id="emailForm" name="Email" placeholder="Coloque seu email de contato! :)">
  <button type="submit" id="btnForm" onclick="emailVerification()">ENVIAR</button>
  
</div>