await_block() — svelte Function Reference

Source Code

packages/svelte/src/internal/client/dom/blocks/await.js lines 34–142

export function await_block(node, get_input, pending_fn, then_fn, catch_fn) {
	if (hydrating) {
		hydrate_next();
	}

	var runes = is_runes();

	var v = /** @type {V} */ (UNINITIALIZED);
	var value = runes ? source(v) : mutable_source(v, false, false);
	var error = runes ? source(v) : mutable_source(v, false, false);

	var branches = new BranchManager(node);

	block(() => {
		var input = get_input();
		var destroyed = false;

		/** Whether or not there was a hydration mismatch. Needs to be a `let` or else it isn't treeshaken out */
		// @ts-ignore coercing `node` to a `Comment` causes TypeScript and Prettier to fight
		let mismatch = hydrating && is_promise(input) === (node.data === HYDRATION_START_ELSE);

		if (mismatch) {
			// Hydration mismatch: remove everything inside the anchor and start fresh
			set_hydrate_node(skip_nodes());
			set_hydrating(false);
		}

		if (is_promise(input)) {
			var restore = capture();
			var resolved = false;

			/**
			 * @param {() => void} fn
			 */
			const resolve = (fn) => {
				if (destroyed) return;

				resolved = true;
				// We don't want to restore the previous batch here; {#await} blocks don't follow the async logic
				// we have elsewhere, instead pending/resolve/fail states are each their own batch so to speak.
				restore(false);
				// Make sure we have a batch, since the branch manager expects one to exist
				Batch.ensure();

				if (hydrating) {
					// `restore()` could set `hydrating` to `true`, which we very much
					// don't want — we want to restore everything _except_ this
					set_hydrating(false);
				}

				try {
					fn();
				} finally {
					unset_context();

					// without this, the DOM does not update until two ticks after the promise
					// resolves, which is unexpected behaviour (and somewhat irksome to test)
					if (!is_flushing_sync) flushSync();
				}
			};

			input.then(
				(v) => {
					resolve(() => {
						internal_set(value, v);
						branches.ensure(THEN, then_fn && ((target) => then_fn(target, value)));
					});
				},
				(e) => {
					resolve(() => {
						internal_set(error, e);
						branches.ensure(THEN, catch_fn && ((target) => catch_fn(target, error)));

						if (!catch_fn) {
							// Rethrow the error if no catch block exists
							throw error.v;
						}
					});
				}
			);