Unable to get property 'match' of undefined or null reference iam using vs2012 so i need client side script for textbox so that first value in textbox be numeric and other are alphabets

Question

User-94139624 posted

 <script type="text/javascript">

            function Validate(event) {

                var address = document.getElementById("address")

                var regex = new RegExp('/^[0-9]{1}[a-zA-Z0-9]$/');

                if (address.match(regex)) {

                    alert("address must begin with a number");

                    return false;

                }

            }

    </script>  

 <asp:TextBox runat="server" ID="txtvalid" onkeypress="return Validate(event);"></asp:TextBox>

Answer 1

User-707554951 posted

Hi Saipavanchandu,

document.getElementById("id ") return An Element Object

match() is used to String object.

So, you need to get the value of Element Object, Then use match().

https://www.w3schools.com/jsref/met_document_getelementbyid.asp

https://www.w3schools.com/jsref/jsref_match.asp

Besides, you should provide correct id for document.getElementById().

Replace “adderss0” with” txtvalid”;

Working code as below:

 <script type="text/javascript">
        function Validate(event) {
            var pattern = /^[0-9]{1}[0-9a-zA-Z]+$/;
                        
            if (!document.getElementById("txtvalid").value.match(pattern))
            {
                alert("address must begin with a number");       
            }
            return false;
        }
    </script>
 <asp:TextBox runat="server" ID="txtvalid" onchange ="return Validate(event);"></asp:TextBox>

Output:



Related links about test method and match method in javascript:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/match

https://websistent.com/javascript-validation-with-regular-expressions/

Best regards

Cathy