JSFiddle - React, Tailwind, and code Playground

HTML

<table align="center">
        <tr>
            <td>

                <input name="firstname"  class="text_area"  maxlength=20 placeholder="Name" type="text" onKeyPress="return onlyAlphabets(event,this)" required  id="ValidName" value="" />
            </td>

            <tr>
            <td>
            <input type="text" onkeypress="return isNumber(event)" id="volpincode" maxlength=7 name="pincode"  value="" required  placeholder="Pincode" class="text_area">
            </td>
            <td><input style="width:300px" type="text" onkeypress="return keyup(event)" class="facebookUrl" name="facebook" value="http://www.facebook.com/$facebook"></td>
            <td>
        <input style="width:30px" disabled="disabled" type="text" name="facebook" value="+91" />
    </td>
            </tr>
        </tr>
    </table>

JavaScript

function onlyAlphabets(e, t) {
            var charCode;
            try {
                if (window.event)  {
                   charCode = window.event.keyCode;
                }
                else if (e) {
                    charCode = e.which;
                }
                else { return true; }
                if (charCode == 8 || (charCode > 64 && charCode < 91) || (charCode > 96 && charCode < 123))
                    return true;
                else
                    return false;
            }
            catch (err) {
                alert(err.Description);
            }
        }

    function isNumber(evt) {
    evt = (evt) ? evt : window.event;
    var charCode = (evt.which) ? evt.which : evt.keyCode;
    if (charCode > 31 && (charCode < 48 || charCode > 57)) {
        return false;
    }
    return true;
}

$('input.facebookUrl').keyup(function(){
    if (
        ($(this).val().length > 0) && ($(this).val().substr(0,24) != 'http://www.facebook.com/')
        || ($(this).val() == '')
        ){
        $(this).val('http://www.facebook.com/');    
    }
});