ASP:Button and ASP:ImageButton

Simple question:
How do I make a JS-function with OnClick for these two types of buttons which directs me to the page "test.aspx" placed at the same path?

<asp:Button ID=si Text=SI Runat=server onClick="newUrl()"></asp:Button>

function newUrl()
{
...
}

Code:

---


function newUrl()
{
document.location.href='test.aspx';
}

---

function newUrl()
{
location.href = (URL)
}