How do I validate a phone number with javascript?

Question

Would someone a little smarter than myself be able to help me with this function? Its purpose is to validate a text input in a form, a phone number field that will only accept 0-9, dash and dot. The HTML calls the function fine.

function validateFeedback() {
    var phone = document.getElementById("phone");
    var validNumber = "0123456789.-";
    for (i = 0; i < phone.length; i++); {
        if (validNumber.indexOf(phone.charAt(i)) == -1); {
            alert("You have entered an invalid phone number");
            return false;
        }
    }
    return true;
}

Thanks so much for any help.

Answer 1

Regular expressions should help ;)

I'm sorry I haven't tried to run this code, but it should be OK.

function validateFeedback(){
    var phone = document.getElementById("phone");
    var RE = /^[\d\.\-]+$/;
    if(!RE.test(phone.value))
    {
        alert("You have entered an invalid phone number");
        return false;
    }
    return true;
}

Answer 2

try like this:

function validateFeedback()
    {
    var phone = document.getElementById("phone");
    var validNumber = "0123456789.-";


    for(i = 0; i < phone.length; i++) {
            if(validNumber.indexOf(phone.charAt(i)) == -1) {
                    alert("You have entered an invalid phone number");
                    return false;
                }
            }

        return true;
    }

there are ; out of place ...