Call Client Script from Code behind ASP.NET

Hello Experts,

I have a Javascript function, which gets called after the button event is processed everything on server. Since, I have lot of validations doing at client side, is it possible I can break the server code once the JS function is called and if no errors continue with the server side execution.Below code get called only after the button event is executed  on server.

 ScriptManager.RegisterClientScriptBlock(Page, Page.GetType(), Guid.NewGuid().ToString(), "Check('" + Msg+ "');", true);

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I need to break the code on server side and execute my Client-Side function and then continue with the remaining server side code.I'm using AJAX Script manager and  button is doing asynchronous postback to the server using update panel.

Thanks,
ASPDEV