I want an ASP.NET function (client side) executed on the MouseOver event of a button. Where do you add an event handler?

Here is a sample

<asp:button id="btn1" runat="server" text="submit" />

Javascript function to be called onMouseOver event

function Samplefunction()
{
    alert('On mouse over event!');
}

In your code behind file you include the following code in Page_Load event handler

btn1.Attributes.Add("onmouseover", "Samplefunction()");