<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/
xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
<title>Ejemplo de código JavaScript en el propio documento</title>

  <script type="text/javascript">
  /**function limita(maximoCaracteres) {
   var elemento = document.getElementById("texto");
   if(elemento.value.length >= maximoCaracteres ) {
     return false;
     }
   else {
     return true;
     }
  }
  **/

  function comprueba(){
  var cuadrotxt = document.getElementById("elemento");
  alert ("value; "+cuadrotxt.value+"\n type: "+cuadrotxt.type+"\n name: "+cuadrotxt.name);
  alert ("elemento2: "+cuadrotxt.form.elemento2.value);
  }

  window.onload=function(){
  if(document.forms.length > 0) {
    if(document.forms[0].elements.length > 0) {
     document.forms[0].elements[0].focus();
    }
  }
  }
  </script>

</head>
<body>
  <form name="formulario" id="formulario" >
    <input type="number" name="elemento" id="elemento" />
    <input type="number" name="elemento2" id="elemento2" />
    
    <textarea id="texto" onkeypress="return limita(100);"></textarea>
    
    <input type="button" value="Enviar" onclick="this.value='enviando...';comprueba()"/>
  </form>
</body>
</html>






<!--this.disabled=true;-->