javascript confirmation dialog box

I have a page with a button and when it is clicked, it will execute a long time task asynchronously. I tried to implement validation on that button using javascript and a confirmation dialog box will pop up when it is clicked. But when i clicked on 'Cancel' in the confirmation dialog box, the long time task still will be executed instead of returning false.

Any idea guys? Any help is appreciated!

Code-Behind:

btnPrint.Attributes.Add("onclick"开发者_开发问答, "javascript:submittingID='btnAdd';return validation();")

Public Sub LongTimeTask()
   .......
End Sub

Javascript:

function validation() {
    ....
    confirmPrint()
}

function confirmPrint() {
        if (confirm("Are you sure you want to print? This process may take up to few minutes.") == true)
            return true;
        else
            return false;
}

validation doesn't return anything. try:

function validation() {
    //...
    return confirmPrint();
}

You can also remove the if from confirmPrint. Doesn't change the behavior, but no need to check for true and return true:

function confirmPrint() {
    return confirm("Are you sure you want to print?");
}

My guess from the description you gave is something like this:

<a href="javascript:if(confirm('Do you want to run this long task?')){ longTask() };">Link Text</a>