File Type and Extension validation for multiple FileUpload controls using CustomValidator in ASP.Net

Hi,

I was referring muddasar's one of the article for the validation. 

Below is my code and i am trying to validate the file upload selected file format on the submit button. I have 4 upload control and  fu1 is mandatory field and others are not mandatory fields. Though i need to validate all the four uploads if the files have been selected. My full sample code is below for easy testing,

<asp:FileUpload runat="server" ID="fu1" />
<asp:Label ID="lblMessage1" runat="server"></asp:Label>
<asp:FileUpload runat="server" ID="fu2" />
<asp:Label ID="lblMessage2" runat="server"></asp:Label>
<asp:FileUpload runat="server" ID="fu3" />
<asp:Label ID="lblMessage3" runat="server"></asp:Label>
<asp:FileUpload runat="server" ID="fu4" />
<asp:Label ID="lblMessage4" runat="server"></asp:Label>

  <asp:Button ID="btnSubmit"  runat="server" ValidationGroup="vgSubmit"
                                     Text = "Validaete" OnClick="btnSubmit_Click" OnClientClick="return ValidateUploads()" />


<script type="text/javascript">
var validFilesTypes = ["bmp", "gif", "png", "jpg"];

    function ValidateUploads() {

        return ValidateUpload1();
        return ValidateUpload2();
        return ValidateUpload3();
        return ValidateUpload4();

    }

function ValidateUpload1() {
        var fu1 = document.getElementById("<%=fu1.ClientID%>");
        var lblMessage1 = document.getElementById("<%=lblMessage1.ClientID%>");
        var fu1path;

        // Check  Upload1 File format
        var fu1path = fu1.value;
        var isValidFile = false;
        if (fu1path != null && fu1path != '') {
            var ext = fu1path.substring(fu1path.lastIndexOf(".") + 1, fu1path.length).toLowerCase();

            for (var i = 0; i < validFilesTypes.length; i++) {
                if (ext == validFilesTypes[i]) {
                    isValidFile = true;
                    break;
                }
            }
            if (!isValidFile) {
                lblMessage1.style.color = "red";
                lblMessage1.innerHTML = "Invalid File. Please upload a File with" +
                 " extension:\n\n" + validFilesTypes.join(", ");
            }
        }

        else { isValidFile = false; }

        return isValidFile;
    }

    function ValidateUpload2() {
        var fu2 = document.getElementById("<%=fu2.ClientID%>");
        var lblMessage2 = document.getElementById("<%=lblMessage2.ClientID%>");
        var fu2path;
        // Check  Upload2 Image Type format
        var fu2path = fu2.value;
        alert(fu2path);
        var isValidFile = false;
        if (fu2path != null && fu2path != '') {
            var ext = fu2path.substring(fu2path.lastIndexOf(".") + 1, fu2path.length).toLowerCase();

            for (var i = 0; i < validFilesTypes.length; i++) {
                if (ext == validFilesTypes[i]) {
                    isValidFile = true;
                    break;
                }
            }

            if (!isValidFile) {
                lblMessage2.style.color = "red";
                lblMessage2.innerHTML = "Invalid File. Please upload a File with" +
                 " extension:\n\n" + validFilesTypes.join(", ");

            }
        }
        else { isValidFile = true; }

        return isValidFile;
    }

    function ValidateUpload3() {
        var fu3 = document.getElementById("<%=fu3.ClientID%>");
        var lblMessage3 = document.getElementById("<%=lblMessage3.ClientID%>");
        var fu3path;
        // Check Product Upload Image Type format
        var fu3path = fu3.value;
        alert(fu3path);
        var isValidFile = false;
        if (fu3path != null && fu3path != '') {
            var ext = fu3path.substring(fu3path.lastIndexOf(".") + 1, fu3path.length).toLowerCase();

            for (var i = 0; i < validFilesTypes.length; i++) {
                if (ext == validFilesTypes[i]) {
                    isValidFile = true;
                    break;
                }
            }
            if (!isValidFile) {
                lblMessage3.style.color = "red";
                lblMessage3.innerHTML = "Invalid File. Please upload a File with" +
                 " extension:\n\n" + validFilesTypes.join(", ");
            }
            else { isValidFile = true; }
        }
        return isValidFile;
    }

    function ValidateUpload4() {

        var fu4 = document.getElementById("<%=fu4.ClientID%>");
        var lblMessage4 = document.getElementById("<%=lblMessage4.ClientID%>");
        var fu4path;

        // Check Ingredients Upload File format

        var fu4path = fu4.value;
        alert(fu4path);
        var isValidFile = false;
        if (fu4path != null && fu4path != '') {
            var ext = fu4path.substring(fu4path.lastIndexOf(".") + 1, fu4path.length).toLowerCase();

            for (var i = 0; i < validFilesTypes.length; i++) {
                if (ext == validFilesTypes[i]) {
                    isValidFile = true;
                    break;
                }
            }
            if (!isValidFile) {
                lblMessage4.style.color = "red";
                lblMessage4.innerHTML = "Invalid File. Please upload a File with" +
                 " extension:\n\n" + validFilesTypes.join(", ");
            }
            else { isValidFile = true; }
        }

        return isValidFile;
    }
</script>

I am doing slight mistake on the return to the main function. if i test indvidual function it works fine. whereas if i include the 4 functions in one function  with the return statement, it's not validating. goes to to the server.

Any suggestions or corrrections please