Function handler

packages/svelte/src/internal/client/reactivity/deriveds.js:211–248

(value, error = undefined)

		 * @param {unknown} error
		 */
		const handler = (value, error = undefined) => {
			if (DEV) {
				reactivity_loss_tracker = null;
			}

			decrement_pending?.();
			deferreds.delete(d);

			if (error === OBSOLETE) return;

			batch.activate();

			if (error) {
				signal.f |= ERROR_VALUE;

				// @ts-expect-error the error is the wrong type, but we don't care
				internal_set(signal, error);
			} else {
				if ((signal.f & ERROR_VALUE) !== 0) {
					signal.f ^= ERROR_VALUE;
				}

				if (DEV && location !== undefined && !signal.equals(value)) {
					recent_async_deriveds.add(signal);

					setTimeout(() => {
						if (recent_async_deriveds.has(signal) && (effect.f & DESTROYED) === 0) {
							w.await_waterfall(/** @type {string} */ (signal.label), location);
							recent_async_deriveds.delete(signal);
						}
					});
				}

				internal_set(signal, value);
			}

			batch.deactivate();
		};

		d.promise.then(handler, (e) => handler(null, e || 'unknown'));
	});