test.js

var scrollLocation;
var freezedScrollLocation;
var dpiX = 15; // standard resolution server-side

function insertComplexElement() {

    // store the current scroll location
    freezedScrollLocation = scrollLocation;
    
    var serviceURL = "/api/TXDocument/InsertComplexElement";

    TXTextControl.saveDocument(TXTextControl.streamType.InternalUnicodeFormat, function (e) {
    
        $.ajax({
            type: "POST",
            url: serviceURL,
            contentType: 'application/json',
            data: JSON.stringify({
                Document: e.data
            }),
            success: successFunc,
            error: errorFunc
        });

        function successFunc(data, status) {

            //disable loading dialog
            TXTextControl.isLoadingDialogEnabled = false;
            TXTextControl.enableCommands(); // enable commands
            
            // code that loads a document that is returned by an endpoint
            TXTextControl.loadDocument(TXTextControl.streamType.InternalUnicodeFormat, data);

            // restore the scroll position
            TXTextControl.sendCommand(TXTextControl.Command.ScrollDelta,
                freezedScrollLocation.location.x * dpiX,
                freezedScrollLocation.location.y * dpiX)
        }

        function errorFunc() {
            console.log("error");
        }
    }
}

TXTextControl.addEventListener("textViewLocationChanged", function (e) {
    scrollLocation = e;
});