myChart.js

function getChartData() {
    $("#loadingMessage").html('<img src="./giphy.gif" alt="" srcset="">');
    $.ajax({
        url: "http://localhost:3000/chartdata",
        success: function (result) {
            $("#loadingMessage").html("");
            var data = [];
            data.push(result.thisWeek);
            data.push(result.lastWeek);
            var labels = result.labels;
            renderChart(data, labels);
        },
        error: function (err) {
            $("#loadingMessage").html("Error");
        }
    });
}

$("#renderBtn").click(
    function () {
        getChartData();
    }
);