how to execute javascript of one page on click in another page

you should not do this. It is insecure.

I am not sure whether this is the solution for your question. You can issue a Server.Transfer to Page A from Page B and pass a context variable also. Check this context variable and then in the Page_Load event you can call the javascript function by using

ClientScript.RegisterClientScriptBlock method

if the calling window opened the called window just use the handle returned from the window.open. otherwise no dice.

First, you need a link to open the new window with a call to the window.open() function, passing it a URL and a target. Pass it '_blank' to inform the browser to use a new window:

Add this link within A.aspx:

<a href="#" onclick="window.open('B.html', '_blank'); return false;">
    New window
</a>

Second, you'll also need a reference to the new window's opener, which is the window which created the new window:

Add this code within B.aspx (please replace FUNCTION_NAME() with your function identifier) to call your parent window's function:

<script type="text/javascript">
    window.opener.FUNCTION_NAME(); // Call FUNCTION_NAME() within A.aspx.
</script>

You can also access window.opener.document to access the original window's DOM.

More information is available here:

Documentation for window.open() function

DOcumentation for window.opener object