index.html
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Show hidden characters
<!DOCTYPE html>
<html lang="en"> <head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Cross Tab Communication</title>
<style>
* {
margin: 0;
padding: 0;
box-sizing: border-box;
overflow: hidden;
}
</style>
</head>
<body>
<canvas id="default"></canvas>
<script src="/index.js"></script>
</body>
</html>
index.js
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Show hidden characters
const TAB_ID = crypto.randomUUID();
const TAB_TIMEOUT = 100;
const channel = new BroadcastChannel('cross-tab-com');
const canvas = document.getElementById('default');
const ctx = canvas.getContext('2d');
const posMap = {};
const lastSeenMap = {};
channel.addEventListener('message', (event) => {
if (event.data.tabId === TAB_ID) return;
posMap[event.data.tabId] = { x: event.data.x, y: event.data.y };
lastSeenMap[event.data.tabId] = performance.now();
});
function getWindowMiddlePosition() {
const chromeHeight = window.outerHeight - window.innerHeight;
return {
x: window.screenX + window.innerWidth / 2,
y: window.screenY + chromeHeight + window.innerHeight / 2,
};
}
function globalToLocal(globalX, globalY) {
const chromeHeight = window.outerHeight - window.innerHeight;
return {
x: globalX - window.screenX,
y: globalY - window.screenY - chromeHeight,
};
}
function post() {
const { x, y } = getWindowMiddlePosition();
channel.postMessage({ tabId: TAB_ID, x, y });
}
function period() {
ctx.clearRect(0, 0, canvas.width, canvas.height);
drawLines();
drawPoints();
requestAnimationFrame(period);
}
function drawLines() {
const currentGlobal = getWindowMiddlePosition();
const currentLocal = globalToLocal(
currentGlobal.x,
currentGlobal.y
);
const points = [{ x: currentLocal.x, y: currentLocal.y }];
for (const id in posMap) {
const remoteGlobal = posMap[id];
const remoteLocal = globalToLocal(remoteGlobal.x, remoteGlobal.y);
points.push({ x: remoteLocal.x, y: remoteLocal.y });
}
ctx.strokeStyle = 'black';
ctx.lineWidth = 1;
for (let i = 0; i < points.length; i++) {
for (let j = i + 1; j < points.length; j++) {
ctx.beginPath();
ctx.moveTo(points[i].x, points[i].y);
ctx.lineTo(points[j].x, points[j].y);
ctx.stroke();
}
}
}
function drawPoints() {
const currentGlobal = getWindowMiddlePosition();
const currentLocal = globalToLocal(
currentGlobal.x,
currentGlobal.y
);
ctx.beginPath();
ctx.arc(currentLocal.x, currentLocal.y, 10, 0, 2 * Math.PI);
ctx.fillStyle = 'red';
ctx.fill();
for (const id in posMap) {
const remoteGlobal = posMap[id];
const remoteLocal = globalToLocal(
remoteGlobal.x,
remoteGlobal.y
);
ctx.beginPath();
ctx.arc(remoteLocal.x, remoteLocal.y, 10, 0, 2 * Math.PI);
ctx.fillStyle = 'blue';
ctx.fill();
}
}
function resizeCanvas() {
canvas.width = window.outerWidth;
canvas.height = window.outerHeight;
}
function cleanupDeadTabs() {
const now = performance.now();
for (const id in lastSeenMap) {
if (now - lastSeenMap[id] > TAB_TIMEOUT) {
delete lastSeenMap[id];
delete posMap[id];
}
}
}
window.addEventListener("resize", resizeCanvas);
resizeCanvas();
period();
setInterval(post, 10);
setInterval(cleanupDeadTabs, 100);
source & further reading
gist.github.com — original article
OpenCode AI config to deny read access to .env, node_modules, build artifacts, cache dirs and ask before bash execution
Download CapCut Pro 2026 for Mac
For Agentic Coding