ws.onmessage = function(event) { Object.keys(cursors).forEach((id) => { if (!positions.find((pos) => pos.id === id)) { document.body.removeChild(cursors[id]); delete cursors[id]; } });
ws.onmessage = function(event) { const positionIds = new Set(positions.map(pos => pos.id)); Object.keys(cursors).forEach((id) => { if (!positionIds.has(id)) { document.body.removeChild(cursors[id]); delete cursors[id]; } }); };