Validation of Telephone Number using Javascript

function telephone_Onchange(fieldname) {

    var targetattribute = Xrm.Page.getAttribute(fieldname);

    var phonenumber = targetattribute.getValue();

    var targetcontrol = Xrm.Page.getControl(fieldname);

    if (phonenumber == null) {

        targetcontrol.clearNotification();

        return;

    }

    if (phonenumber.length == 0) {

        targetcontrol.clearNotification();

        return;

    }

    phonenumber = phonenumber.replace(/\+/g, "");

    phonenumber = phonenumber.replace(/\(/g, "");

    phonenumber = phonenumber.replace(/\)/g, "");

    phonenumber = phonenumber.replace(/\-/g, "");

    phonenumber = phonenumber.replace(/\s/g, "");

    phonenumber = phonenumber.replace(/\./g, "");

    if (isNaN(phonenumber) || phonenumber.length < 10 || phonenumber.length > 12) {

        targetcontrol.setNotification("Telephone number not validIt ");

        return;

    }

    targetcontrol.clearNotification();

}