What causes "Live query completed before yielding a value" in sveltejs/kit?

Ensure the server generator always yields an initial value before any early return

Live query completed before yielding a value

Error message

Live query completed before yielding a value

What it means

A query.live generator must yield at least one value before completing. If the server-side async generator returns (done: true) before the client has received its first value and the query was never ready, SvelteKit throws because there is no value to expose to consumers.

Source

Thrown at packages/kit/src/runtime/client/remote-functions/query-live/instance.svelte.js:148

			this.#interrupt = () => {
				controller.abort();
				return stopped;
			};

			const generator = create_live_iterator(this.#id, this.#payload, controller, () => {
				this.#connected = true;
				this.#attempt = 0;
				connected = true;
				on_connect();
			});

			try {
				const { done, value } = await generator.next();

				if (done) {
					if (!this.#ready) {
						throw new Error('Live query completed before yielding a value');
					}
					// stream completed without yielding (e.g. the generator returned
					// immediately on reconnect) — keep the last good value
					this.#done = true;
					this.#fan_out.done();
					break;
				}

				this.set(value);

				for await (const value of generator) {
					this.set(value);
				}

				this.#done = true;
				this.#fan_out.done();
			} catch (error) {
				if (controller.signal.aborted) break;

View on GitHub (pinned to 03f1687fe6)

Solutions

Ensure the server generator always yields an initial value before any early return
Check the generator body for early returns/throws before the first yield
Wrap generator logic so reconnects still yield the current value
Log server-side to confirm the generator body actually runs

Example fix

// before
export async function *live() {
  if (!ready) return; // completes without yielding
  yield getData();
}
// after
export async function *live() {
  yield getData(); // always yield at least once
  while (ready) {
    await changes.next();
    yield getData();
  }
}

Defensive patterns

Strategy: try-catch

Try / catch

try {
  await liveQuery.current;
} catch (e) {
  if (e.message === 'Live query completed before yielding a value') {
    // fall back to a regular query or show empty state
  } else throw e;
}

Prevention

Always yield an initial value in live query generators
Avoid early returns before the first yield
Test reconnect paths to ensure a value is yielded

When it happens

Trigger: A live query's server generator returns immediately (e.g. an early return, an unhandled condition, or a reconnect handler that returns without yielding) so the client's generator.next() resolves done while #ready is still false.

Common situations: Server generator whose first statement is a conditional return; generator that only yields after an event that never fires; reconnect logic that returns early when no data has changed yet; abrupt completion due to an error swallowed upstream.

Related errors

AI-assisted analysis of sveltejs/kit@03f1687fe6 (2026-09-02). Data as JSON: /api/errors/5bb19a349821e6f3. Report an issue: GitHub.