javascript - Asp.net add form onsubmit() from code behind -

how can modify onsubmit parameter of form master page asp.net project in code behind of child page?

i update form value this:

<form id="form1" runat="server" onsubmit="setpostbackvalues()"> 

try below -

((system.web.ui.htmlcontrols.htmlform) master.findcontrol("form1")).attributes.add("onsubmit",             "javascript:return setpostbackvalues();");