flush_queued_effects() — svelte Function Reference

Source Code

packages/svelte/src/internal/client/reactivity/batch.js lines 685–751

function flush_queued_effects(effects) {
	var length = effects.length;
	if (length === 0) return;

	var i = 0;

	while (i < length) {
		var effect = effects[i++];

		if ((effect.f & (DESTROYED | INERT)) === 0 && is_dirty(effect)) {
			eager_block_effects = new Set();

			update_effect(effect);

			// Effects with no dependencies or teardown do not get added to the effect tree.
			// Deferred effects (e.g. `$effect(...)`) _are_ added to the tree because we
			// don't know if we need to keep them until they are executed. Doing the check
			// here (rather than in `update_effect`) allows us to skip the work for
			// immediate effects.
			if (effect.deps === null && effect.first === null && effect.nodes === null) {
				// if there's no teardown or abort controller we completely unlink
				// the effect from the graph
				if (effect.teardown === null && effect.ac === null) {
					// remove this effect from the graph
					unlink_effect(effect);
				} else {
					// keep the effect in the graph, but free up some memory
					effect.fn = null;
				}
			}

			// If update_effect() has a flushSync() in it, we may have flushed another flush_queued_effects(),
			// which already handled this logic and did set eager_block_effects to null.
			if (eager_block_effects?.size > 0) {
				old_values.clear();

				for (const e of eager_block_effects) {
					// Skip eager effects that have already been unmounted
					if ((e.f & (DESTROYED | INERT)) !== 0) continue;

					// Run effects in order from ancestor to descendant, else we could run into nullpointers
					/** @type {Effect[]} */
					const ordered_effects = [e];
					let ancestor = e.parent;
					while (ancestor !== null) {
						if (eager_block_effects.has(ancestor)) {
							eager_block_effects.delete(ancestor);
							ordered_effects.push(ancestor);
						}
						ancestor = ancestor.parent;
					}

					for (let j = ordered_effects.length - 1; j >= 0; j--) {
						const e = ordered_effects[j];
						// Skip eager effects that have already been unmounted
						if ((e.f & (DESTROYED | INERT)) !== 0) continue;
						update_effect(e);
					}
				}

				eager_block_effects.clear();
			}
		}
	}

	eager_block_effects = null;
}