internal_set() — svelte Function Reference

Source Code

packages/svelte/src/internal/client/reactivity/sources.js lines 174–259

export function internal_set(source, value) {
	if (!source.equals(value)) {
		var old_value = source.v;

		if (is_destroying_effect) {
			old_values.set(source, value);
		} else {
			old_values.set(source, old_value);
		}

		source.v = value;

		var batch = Batch.ensure();
		batch.capture(source, old_value);

		if (DEV) {
			if (tracing_mode_flag || active_effect !== null) {
				source.updated ??= new Map();

				// For performance reasons, when not using $inspect.trace, we only start collecting stack traces
				// after the same source has been updated more than 5 times in the same flush cycle.
				const count = (source.updated.get('')?.count ?? 0) + 1;
				source.updated.set('', { error: /** @type {any} */ (null), count });

				if (tracing_mode_flag || count > 5) {
					const error = get_error('updated at');

					if (error !== null) {
						let entry = source.updated.get(error.stack);

						if (!entry) {
							entry = { error, count: 0 };
							source.updated.set(error.stack, entry);
						}

						entry.count++;
					}
				}
			}

			if (active_effect !== null) {
				source.set_during_effect = true;
			}
		}

		if ((source.f & DERIVED) !== 0) {
			const derived = /** @type {Derived} */ (source);

			// if we are assigning to a dirty derived we set it to clean/maybe dirty but we also eagerly execute it to track the dependencies
			if ((source.f & DIRTY) !== 0) {
				execute_derived(derived);
			}

			update_derived_status(derived);
		}

		source.wv = increment_write_version();

		// For debugging, in case you want to know which reactions are being scheduled:
		// log_reactions(source);
		mark_reactions(source, DIRTY);

		// It's possible that the current reaction might not have up-to-date dependencies
		// whilst it's actively running. So in the case of ensuring it registers the reaction
		// properly for itself, we need to ensure the current effect actually gets
		// scheduled. i.e: `$effect(() => x++)`
		if (
			is_runes() &&
			active_effect !== null &&
			(active_effect.f & CLEAN) !== 0 &&
			(active_effect.f & (BRANCH_EFFECT | ROOT_EFFECT)) === 0
		) {
			if (untracked_writes === null) {
				set_untracked_writes([source]);
			} else {
				untracked_writes.push(source);
			}
		}

		if (!batch.is_fork && eager_effects.size > 0 && !eager_effects_deferred) {
			flush_eager_effects();