render_chart = (svg, data) => {
const t1 = svg.transition().duration(1000);
const t2 = svg.transition().duration(2000);
svg.selectAll('rect')
.data(data)
.join(
enter => enter.append("rect")
.attr("x", (d, i) => (i * (10 + 2) ))
.attr("y", 0)
.attr("width", 10)
.attr("height", 10)
.attr("fill", (d, i) => 'blue'),
update => update.transition(t1).attr('fill', pickColor()),
exit => exit.transition(t2).attr('fill', 'white').remove()
);
}