Hola, cyber
Ahí va:
Código HTML:
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<script language="javascript" type="text/javascript">
function valida(tx)
{ var nMay = 0, nMin = 0, nNum = 0
var t1 = "ABCDEFGHIJKLMNÑOPQRSTUVWXYZ"
var t2 = "abcdefghijklmnñopqrstuvwxyz"
var t3 = "0123456789"
for (i=0;i<tx.length;i++) {
if ( t1.indexOf(tx.charAt(i)) != -1 ) {nMay++}
if ( t2.indexOf(tx.charAt(i)) != -1 ) {nMin++}
if ( t3.indexOf(tx.charAt(i)) != -1 ) {nNum++}
}
if ( nMay>0 && nMin>0 && nNum>0 ) { return true }
else { return false }
}
</script>
</head>
<body>
<form>
<input type="text" name="texto1">
<input type="button" value="Validar" onClick="alert(valida(this.form.texto1.value))">
</form>
</body>
</html>