ondrain(drainable)

• drainable <Object> 实现了可排水协议的对象。
• 返回：<Promise> | <null>

等待可排空的写入器恢复物理缓冲区容量。如果对象未实现可排空协议，则返回 null；或者返回一个承诺，当缓冲数据低于字节预算时，承诺会以 true 完成。

🌐 Wait for a drainable writer to regain physical buffer capacity. Returns null if the object does not implement the drainable protocol, or a promise that fulfills with true when buffered data falls below the byte budget.

对于使用 'drop-oldest' 或 'drop-newest' 的写入者来说，这会等待物理容量，即使写入不会阻塞。这允许生产者在写入前等待，从而避免数据丢失。

🌐 For writers using 'drop-oldest' or 'drop-newest', this waits for physical capacity even though writes do not block. This allows producers to avoid data loss by waiting before writing.

import { push, ondrain, text } from 'node:stream/iter';

const { writer, readable } = push({ budget: 16384 });
const chunk = new Uint8Array(8192);  // 8 KB
writer.writeSync(chunk);
writer.writeSync(chunk);  // 16 KB total -- buffer full

// Start consuming so the buffer can actually drain
const consuming = text(readable);

// Buffer is full -- wait for drain
const canWrite = await ondrain(writer);
if (canWrite) {
  await writer.write('c');
}
await writer.end();
await consuming;const { push, ondrain, text } = require('node:stream/iter');

async function run() {
  const { writer, readable } = push({ budget: 16384 });
  const chunk = new Uint8Array(8192);  // 8 KB
  writer.writeSync(chunk);
  writer.writeSync(chunk);  // 16 KB total -- buffer full

  // Start consuming so the buffer can actually drain
  const consuming = text(readable);

  // Buffer is full -- wait for drain
  const canWrite = await ondrain(writer);
  if (canWrite) {
    await writer.write('c');
  }
  await writer.end();
  await consuming;
}

run().catch(console.error);拷贝