Deno KV watch

在 Github 上编辑

Warning: This is an unstable API that is subject to change or removal at anytime.
Deno KV watch allows you to detect changes to your KV database, making it easier to build real-time applications, newsfeeds, chat, and more.

Open the default database

const kv = await Deno.openKv();

Set "counter" value to 0, then increment every second.

await kv.set(["counter"], new Deno.KvU64(0n));
setInterval(() => {
  kv.atomic().sum(["counter"], 1n).commit();
}, 1000);

Listen for changes to "counter" and log value.

for await (const [entry] of kv.watch([["counter"]])) {
  console.log(`Counter: ${entry.value}`);
}

You can also create a stream reader from kv.watch, which returns a ReadableStream.

const stream = kv.watch([["counter"]]).getReader();
while (true) {
  const counter = await stream.read();
  if (counter.done) {
    break;
  }
  console.log(`Counter: ${counter.value[0].value}`);
}

To use server-sent events, let's create a server that responds with a stream. Each time a change to "counter" is detected, send the updated value to the client.

Deno.serve((_req) => {
  const stream = kv.watch([["counter"]]).getReader();
  const body = new ReadableStream({
    async start(controller) {
      while (true) {
        if ((await stream.read()).done) {
          return;
        }
        const data = await kv.get(["counter"]);
        controller.enqueue(
          new TextEncoder().encode(`Counter: ${data.value}\n`),
        );
      }
    },
    cancel() {
      stream.cancel();
    },
  });
  return new Response(body, {
    headers: {
      "Content-Type": "text/event-stream",
    },
  });
});

使用 Deno CLI 在本地运行此示例：

deno run --unstable-kv https://docs.denohub.com/examples/scripts/kv_watch.ts

Deno KV watch

Additional resources

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