Validating Phone Numbers Using Javascript

Question

I'm working on a web form with several fields and a submit button. When the button is clicked, I am to verify that the required text boxes have been filled in and that the phone number is in the correct format. I can only accept 7 or 10 digit phone numbers, but characters such as (,), (-), etc are acceptable. If this box is empty or the phone number isn't in the correct format (not 7 or 10 numbers long, not a number) or has been left blank, I am supposed to add a red border around the text box. This border is supposed to remain in place until the user corrects the error.

I can't get this to work properly. I have tried several different ways to go about doing this, but have gotten several different types of errors. One way seemed to work, but the red border only displayed for a second and then disappeared and the value in the textbox was reset.

Here is my code and a link to a jsfiddle I've created:

Javascript:

<script type="text/javascript">
    function validateForm() {
        return checkPhone();
    }
    function checkPhone() {
        var phone = document.forms["myForm"]["phone"].value;
        var phoneNum = /^\(?([0-9]{3})\)?[-. ]?([0-9]{3})[-. ]?([0-9]{4})$/; 
            if(phone.value.match(phoneNum)) {
                return true;
            }
            else {
                document.getElementById("phone").className = document.getElementById("phone").className + " error";
                return false;
            }
        }
</script>

HTML:

<form name="myForm" onsubmit = "return validateForm()">
    Phone Number: <input type="text" id="phone"><br>
</form>

JSFiddle:

http://jsfiddle.net/mkdsjc0p/

Answer 1

function telephoneCheck(str) {
  var a = /^(1\s|1|)?((\(\d{3}\))|\d{3})(\-|\s)?(\d{3})(\-|\s)?(\d{4})$/.test(str);
  alert(a);
}
telephoneCheck("[phone]");

Where str could be any of these formats: 555-555-5555 [phone] [phone] 555 555 5555 5555555555 1 555 555 5555