var numbers="0123456789.";
  function isNumeric(x) {
    // is x a String or a character?
    if(x.length>1) {
      // remove negative sign
      x=Math.abs(x)+"";
      for(j=0;j<x.length;j++) {
        // call isNumeric recursively for each character
        number=isNumeric(x.substring(j,j+1));
        if(!number) return number;
      }
      return number;
    }
    else {
      // if x is number return true
      if(numbers.indexOf(x)>=0) return true;
      return false;
    }
  }
  
function checkTxt(obj,longitud){
	if(obj.value.length>longitud){
		alert('El campo tiene un máximo de ' + longitud + ' caracteres')
		obj.value=obj.value.substring(0,longitud)
	}
}
function validar_correo (correo){
	if(correo != "") {
		emailad = correo;
		var exclude=/[^@\-\.\w]|^[_@\.\-]|[\._\-]{2}|[@\.]{2}|(@)[^@]*\1/;
		var check=/@[\w\-]+\./;
		var checkend=/\.[a-zA-Z]{2,4}$/;	
		if(((emailad.search(exclude) != -1)|| (emailad.search(check)) == -1)|| (emailad.search(checkend) == -1)) {
			return false;
		}
		else{
			return true;
		}
	}
}