HTML/Java - How to restrict first 3 number of tel input field to specific number?

Question

I try to make registration site on wordpress that also required SMS phone verification. The problem is that my website is related to Pakistan. I also want to register users that are from Pakistan. But SMS gateway can send sms to world wide, so every one can register. Now I want that when user write phone number in this field:

<input type="tel" name="user_phone" id="user_phone" class="input" value="" size="25">

the first three numbers must be "923". Either this pre-written in input field, user can not change/remove them or on submit user get error of "Invalid number format, number must start with 932". How it possible? You can check its example site at http://goo.gl/SSst3 I hope you will understand what I want to do.

Answer 1

How does this sound :

function validate(elem)
        {
            var anum=/(^923(\d){10}$)/; //using this regex after the number 923 
                                        // we are allowed to have 10 digits 
            if(anum.test(elem.value) == true)
            {
                elem.style.border="2px solid #0F0"; //green light
            }
            else
            {
                elem.style.border="2px solid #F00"; //red light
            }
        }

And in the html we have :

<input type="text" id="phone" onchange="validate(this)" />

Answer 2

php can do this.. run a php script. try reading my notes on php they have good examples to wat you want

read:

https://docs.google.com/file/d/0B-C0T_-acxRqamV4Y1pnUnZtenc/edit?usp=sharing

Answer 3

Use javascript validation:

On form submit have validation which checks for this:

var s = $("#phonenumber").val()

if(s.substr(0, 3)) == "923"
{
    form.submit();
}
else
{
    alert("Invalid number format, number must start with 932");
    return false;
}

Answer 4

Create 2 input fields, one readonly and the other editable.

<input type="telprefix" name="user_phone" id="user_phone_pref" class="input" value="932" size="5" tabindex="20" readonly="readonly"/>
<input type="tel" name="user_phone" id="user_phone" class="input" value="" size="20" tabindex="25" />