WebSocket 心跳与重连：最小客户端策略

let ws, timer, retry=0;
function connect(){
  ws = new WebSocket('wss://example.com/ws');
  ws.onopen = ()=>{ retry=0; timer = setInterval(()=>ws.send('PING'), 10000); };
  ws.onmessage = e=>{ if(e.data==='PONG'){ /* ok */ } };
  ws.onclose = ()=>{ clearInterval(timer); setTimeout(connect, Math.min(30000, 1000 * 2 ** retry++)); };
  ws.onerror = ()=> ws.close();
}
connect();