chart.update(). Enable Chart.js under Libraries, wait until it is checked, then paste the whole editor.

Goal

Run every block and confirm the chart is visible.

document.body.innerHTML = '<canvas id="c" width="420" height="260"></canvas>';
const ch = new Chart(document.getElementById("c"), {
  type: "bar",
  data: { labels: ["Nairobi", "Mombasa", "Kisumu", "Nakuru", "Eldoret"], datasets: [{ label: "units", data: [21, 15, 15, 18, 12] }] },
  options: { responsive: false }
});
ch.data.datasets[0].data = [25, 15, 15, 18, 12];
ch.update();
console.log("updated Nairobi");

document.body.innerHTML = '<canvas id="c" width="420" height="260"></canvas>';
new Chart(document.getElementById("c"), {
  type: "bar",
  data: { labels: ["Nairobi", "Mombasa", "Kisumu", "Nakuru", "Eldoret"], datasets: [{ label: "units", data: [21, 15, 15, 18, 12], backgroundColor: "#1d4f7a" }] },
  options: { responsive: false }
});
console.log("bar again");

document.body.innerHTML = '<canvas id="c" width="420" height="260"></canvas>';
new Chart(document.getElementById("c"), {
  type: "line",
  data: { labels: ["Jan", "Feb", "Mar", "Apr"], datasets: [{ label: "Nairobi", data: [48, 55, 92, 150] }] },
  options: { responsive: false }
});
console.log("line");

console.log('update');