how to prevent postback by javascript

Question

actually this code is working well in firefox mozilla but it's not working in IE8

<asp:Button ID="btnSubmit" runat="server" Text="Submit" CssClass="btnPrimary" OnClientClick="return doSubmit('this');"
        OnClick="btnSubmit_Click" />
      <script type="text/javascript">
           function doSubmit() 
           {
            var ansLength = oDOM.body.innerText.trim().length;
            if (ansLength == 0 && smielyPresent == -1) 
              {
              alert("you cannot submit blank answer");
              return false;
              }
           }
    </script>

     protected void btnSubmit_Click(object sender, EventArgs e)
    {
      // i am doing some stuff
    }

here i want to prevent postback when answerlength == 0 ; but when answer length ==0 then it alert alert("u can't submit blank answer") message and postback to server io want to prevent it how i do ?

Answer 1

It's not working since you have a script error in your javascript.

<script type="text/javascript">
    function doSubmit() 
    {
        //I've removed the first equal sign
        var ansLength = oDOM.body.innerText.trim().length; 
        if (ansLength == 0 && smielyPresent == -1) //typo on smielyPresent ?
        {
            alert("u can't submit blank answer")
            return false;
        }
    }
</script>

Answer 2

try this

OnClientClick="doSubmit(this); return false;"