using WinJS._Signal

_signal.js

 var loadedSignal = new WinJS._Signal();
    document.addEventListener("load", function () { loadedSignal.complete(); });
 
    function loadDataAsync() {
        return WinJS.xhr("uri");
    }
 
    //setup code
    loadedSignal.promise
        .then(loadDataAsync)
        .then(processData);