function isNotEmpty(elem) {
  var str = elem.value;
    var re = /.+/;
    if(!str.match(re)) {
        alert("Vul alstublieft uw telefoonnummer in.");
        setTimeout("focusElement('" + elem.form.name + "', '" + elem.name + "')", 0);
        return false;
    } else {
        return true;
    }
}
function isNumber(elem) {
  var str = elem.value;
    var re = /^[-]?\d*\.?\d*$/;
    str = str.toString();
    if (!str.match(re)) {
        alert("Uw telefoonnummer mag alleen uit getallen bestaan.");
        setTimeout("focusElement('" + elem.form.name + "', '" + elem.name + "')", 0);
        return false;
    }
    return true;
}
function isLen10(elem) {
  var str = elem.value;
    var re = /\b.{10}\b/;
    if (!str.match(re)) {
        alert("Uw telefoonnummer moet uit 10 getallen bestaan.");
        setTimeout("focusElement('" + elem.form.name + "', '" + elem.name + "')", 0);
        return false;
    } else {
        return true;
    }
}
function focusElement(formName, elemName) {
    var elem = document.forms[formName].elements[elemName];
    elem.focus();
    elem.select();
}
function validateForm(form) {
    if (isNotEmpty(form.telefoon)) {
        if (isNumber(form.telefoon)) {
            if (isLen10(form.telefoon)) {
                return true;
            }
        }
    }
    return false;
}