How to block server side event firing under button click in javascript?

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I want to block server side event firing under button click in JavaScript. I have set a JavaScript function in onclientclickevent() and even if it return false set after showing the validation server event is getting fired. The sample code is below.

What I have tried:

Code is as below:

JavaScript

function Test() {
               var regex = /^(?=.*\d)(?=[^A-Za-z]*[A-Za-z])(?=.*[-!@#$%._]).{8,20}$/

               //Validate TextBox value against the Regex.
               var isValid = regex.test(document.getElementById('<%=txtNewPass.ClientID %>').value);
               alert(isValid);
               if (!isValid) {
                   alert("Password must be at least 8 characters, and must include at least one special character, one alphabet, and one numeric digit.");
                   return;
               }

       }

ASP.NET

<asp:Button ID="btnSave" runat="server" Style="position: static" Text="Save" Enabled="true"
                                   Width="111px" CssClass="NeST_BUTTON"  OnClick="btnSave_Click" Height="26px" OnClientClick="javascript:Test();"/>

Posted 31-Jan-22 19:30pm

Member 15421351

Updated 1-Feb-22 5:32am

Sean Ewington

v2

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Richard Deeming · Answer 1 · 2022-01-31T22:35:00

If you want to stop the button from submitting the form, then you need to block the form from being submitted.

ASPX

OnClientClick="Test(event);"

JavaScript

function Test(event){
    ...
    if (!isValid) {
        alert("...");
        event.preventDefault();
        return;
    }
}

Event.preventDefault() - Web APIs | MDN[^]

However, you don't need custom Javascript to validate that an entered value matches a particular regular expression; just use a RegularExpressionValidator instead:

ASPX

<asp:RegularExpressionValidator runat="server"
    ControlToValidate="txtNewPass"
    ValidationExpression="(?=.*\d)(?=[^A-Za-z]*[A-Za-z])(?=.*[-!@#$%._]).{8,20}"
    ErrorMessage="Password must be at least 8 characters, ..."
/>

RegularExpressionValidator Class (System.Web.UI.WebControls) | Microsoft Docs[^]