how can i call a javascript function when an ASP.net validation summary is filled

You will want to call the javascript function Page_ClientValidate() to initiate the ASP.NET validation wired to your page controls. Once this is called, the Page_IsValid boolean value will be properly set.

Here is an example of how I am using it. If ASP.NET validation is successful, I disable the button, otherwise the button remains enabled and the validation summary is displayed to the user. The OnClientClick is from a ASP:Button control.

OnClientClick="javascript:Page_ClientValidate(); if (Page_IsValid==true) { this.disabled=true; }"

I don't think that's possible. It is, however, possible to intercept validation by setting OnClientClick on the controls that do postbacks. Then you can check the global JavaScript variable Page_IsValid for the validation result.

One thing to keep in mind is that, when there are no validators on a page, Page_IsValid will be undefined.

I started to implement the solution by @EverettEvola but also where the validation logic was being called multiple times and displaying multiple ValidationSummary popups. My solution was as follows:

On the button (in my case the button was a submit button)

OnClientClick="return CustomValidationOnClick()"

And the CustomValidationOnClick()

function CustomValidationOnClick(source, args) {

    //Manually kickoff page validation
    //This call will display the Validation summary popup if page is invalid
    Page_ClientValidate();

    //Page_IsValid set by the result of the Page_ClientValidate() call
    if (Page_IsValid == true) {
        this.disabled=true;
        return true; //if Submit button return true to continue form submit
    }
    else {
       //do whatever here
       return false; //if Submit button return false to cancel form submit
    }
}