Validate Input Phone Number in Microsoft Dynamics CRM using JavaScript

Sometime we get requirement to validate a phone number like to check only numeric value allowed with all round bracket and '+' sign etc in the number. So below is a basic JavaScript fucntion which validates a phone number like: (022)6655-7878 or +91-7878787878 or +44-6756-6767-4234 and so on

function CheckPhoneNoFormat(context) {
    var oField = context.getEventSource().getValue();
    if (typeof (oField) != "undefined" && oField != null) {
        try {
            var telnum = oField;

            // Convert into a string and check that we were provided with something
            var telnum = telnum + " ";
            if (telnum.length == 1) {
                telNumberErrorNo = 1;
                return false
            }
            telnum.length = telnum.length - 1;

            // Remove spaces from the telephone number to help validation
            while (telnum.indexOf(" ") != -1) {
                telnum = telnum.slice(0, telnum.indexOf(" ")) + telnum.slice(telnum.indexOf(" ") + 1)
            }

            // Remove hyphens from the telephone number to help validation
            while (telnum.indexOf("-") != -1) {
                telnum = telnum.slice(0, telnum.indexOf("-")) + telnum.slice(telnum.indexOf("-") + 1)
            }

            // Remove hyphens from the telephone number to help validation
            while (telnum.indexOf(")") != -1) {
                telnum = telnum.slice(0, telnum.indexOf(")")) + telnum.slice(telnum.indexOf(")") + 1)
            }

            while (telnum.indexOf("(") != -1) {
                telnum = telnum.slice(0, telnum.indexOf("(")) + telnum.slice(telnum.indexOf("(") + 1)
            }

            while (telnum.indexOf("+") != -1) {
                telnum = telnum.slice(0, telnum.indexOf("+")) + telnum.slice(telnum.indexOf("+") + 1)
            }

            var phoneRegex = telnum.replace(/[^0-9]/g, "");

            if (phoneRegex.length == telnum.length) {
                context.getEventSource().setValue(oField);
                return true;
            }

            else {
                alert("Invalid Number. Please Enter Again");
                context.getEventSource().setValue('');
                return false;
            }
        }
        catch (err) { alert("Some Error Occured. " + err); return false; }
    }
}