Submit button and Javascript

I have a Submit button with code behind that evaluates stuff in c#, the problem is that I also want to add a function in javascript that asks "This file already exists, do you want to replace it?

So my question is how can I trigger both? 开发者_运维技巧

OnClick="myC#mehod" and also OnClientClick =  return (some javascript);

Can I do this?...

deleteBtn.Attributes["onClick"] = 
    "return confirm('This file already exists, do you want to replace it?');"

Updated for clarification;

<asp:Button ID="btnReplace" runat="server" onclick="btnReplace_Click" Text="Button" OnClientClick="return confirm('This file already exists, do you want to replace it?');" />

protected void btnReplace_Click(object sender, EventArgs e)
{
//Replace the File
}

OnClientClick="return confirm('This file already exists, do you want to replace it?');" 

OnClientClick = "if(!confirm('This file already exists, do you want to replace it?')) return false;"

this is more safer than return direct