Código:
<html>
<head>
<script>
function valida(user){
var expregular = /([A-Z+ a-z+ 0-9]{8})/;
if (expregular.test(user)){
alert ('Ingresando');
} else {
alert ('Error');
}
}
function valida(pass){
var expregular2 = /([A-Z+ a-z+ 0-9]{8})/;
if (expregular2.test(pass)){
alert ('Ingresando');
} else {
alert ('Error');
}
}
</script>
</head>
<body bgcolor="#000000">
<font color="#FFFFFF">
<body>
<form>
<center>
<label> Username: </label>
<Input type= "Text" name = "user">
<br>
<label> Password: </label>
<Input type= "Text" name = "pass">
</br>
<Input type= "Button" name= "BotonEntrar" Value="Entrar" onclick = "valida(pass.value)">
</center>
</form>
</body>
</html>