js

getCoalescedEvents()

html

<canvas id="target" width="600" height="300"></canvas>

js

const canvas = document.getElementById("target");
const ctx = canvas.getContext("2d");

const pointerEvents = [];

function drawCircle(x, y, color) {
  ctx.clearRect(0, 0, canvas.width, canvas.height);

  // draw the last 20 events
  if (pointerEvents.length > 20) {
    pointerEvents.shift();
  }
  pointerEvents.push({ x, y, color });

  for (const pointerEvent of pointerEvents) {
    ctx.beginPath();
    ctx.arc(pointerEvent.x, pointerEvent.y, 10, 0, 2 * Math.PI);
    ctx.strokeStyle = pointerEvent.color;
    ctx.stroke();
  }
}

canvas.addEventListener("pointermove", (e) => {
  // draw a circle for the current event
  drawCircle(e.clientX, e.clientY, "black");

  const coalescedEvents = e.getCoalescedEvents();
  for (let coalescedEvent of coalescedEvents) {
    // give it an offset so we can see the difference and color it red
    drawCircle(coalescedEvent.clientX + 20, coalescedEvent.clientY + 20, "red");
  }
});