I am trying to update my d3 bubble chart with new data getting from the backend. However, it seems that the new data gets added to the chart but the old data points are not removed? What is the issue here? Here is my function:

function updateGeoData(ds, de) {
        console.log("hit 233")
        const size = d3.scaleLinear()
            .domain([1, 100])  // What's in the data
            .range([4, 50])  // Size in pixel
        let updateData = $.get("/update_geo_data", {"ds":ds, "de":de});
        updateData.done(function (result) {
            var circles = svg.selectAll("myCircles").data(result, function(d) { return d; });
            circles.attr("class", "update");
            circles.enter().append("circle")
                .merge(circles)
                    .attr("cx", d => projection([d.long, d.lat])[0])
                    .attr("cy", d => projection([d.long, d.lat])[1])
                    .attr("r", d => size(d.count))
                    .style("fill", "69b3a2")
                    .attr("stroke", "#c99614")
                    .attr("stroke-width", 2)
                    .attr("fill-opacity", .4);
            circles.exit().remove();
        });
}