JSFiddle - React, Tailwind, and code Playground

HTML

<script>
function validar(){
      var allOk = true;
			if(document.getElementsByName('Nome')[0].value == '')
			{
				alert("Falta nome");
				allOk = false;
			}
			
			if(!isNaN(document.getElementsByName('NumeroBI')[0].value))
			{
				alert("Sรณ numeros");
				allOk = false;
			}
			else if (document.getElementsByName('NumeroBI')[0].value.length < 8)
			{
				alert("Faltam numeros");
				allOk = false;
			}
			
			if(document.getElementsByName('Email')[0].value.indexOf('@') < 0)		{
				alert("Email Invalido");
				allOk = false;
			}
		return allOk;
		}
</script>
<form action="NovoCliente.php" method="post" onsubmit="return validar();">



<p><label class="formulario">Nome </label><input type="text" name="Nome" size="50" maxlength="30"></p>

<p><label class="formulario">Password </label><input type="password" name="Password" size="50" maxlength="30"></p>

<p><label class="formulario">Número de BI </label><input type="Number" name="NumeroBI" size="50" maxlength="30"></p>

<p><label class="formulario">Morada </label><input type="text" name="Morada" size="50" maxlength="30"></p>

<p><label class="formulario">Telefone </label><input type="text" name="Telefone" size="50" maxlength="30"></p>

<p><label class="formulario">Data de Nascimento </label><input type="Date" name="DataNasc"></p>


<p><label class="formulario">Email </label><input type="text" name="Email" size="50" maxlength="30"></p>


<input type="reset" value="Limpar">
<input type="submit">
</form>