greasemonkey - Execute javascript after page loaded and the page (intern) javascript finished -

i looking function/methode execute javascript (using greasemonkey) after page loaded , page javascript finished.

already tried following ways running testscript after page loaded but before javascript finishs.

    window.onload = function () { testscript() }      window.addeventlistener('load', function () {  testscript()}) 

thanks.