pass the list values from Flask to JS: TypeError--: Object of type 'Undefined' is not JSON serializable cannot be resolved

I am trying to send a list generated in Flask to Javascript. But I kept having this same issue. TypeError: Object of type 'Undefined' is not JSON serializable

Please help me.

My flask code is:

jsonString = json.dumps(LstSNV.serialize())
return render_template("spatial.html", AO_sDocument=occu, snvLst=jsonString)

My js in html page is:

let dataset = {{snvLst|tojson|safe}};

I even try to get the list directly from the html but failed.

            function myFunction() {
                var oldValue = document.getElementById('submit').value;
                console.log(JSON.stringify(oldValue));
                document.getElementById("submit").innerHTML = "LOADING...";
            }

I think this problem is my list is undefined but i dont know how to convert it. Thank you.