head() — svelte Function Reference

Source Code

packages/svelte/src/internal/client/dom/blocks/svelte-head.js lines 12–59

export function head(hash, render_fn) {
	// The head function may be called after the first hydration pass and ssr comment nodes may still be present,
	// therefore we need to skip that when we detect that we're not in hydration mode.
	let previous_hydrate_node = null;
	let was_hydrating = hydrating;

	/** @type {Comment | Text} */
	var anchor;

	if (hydrating) {
		previous_hydrate_node = hydrate_node;

		var head_anchor = get_first_child(document.head);

		// There might be multiple head blocks in our app, and they could have been
		// rendered in an arbitrary order — find one corresponding to this component
		while (
			head_anchor !== null &&
			(head_anchor.nodeType !== COMMENT_NODE || /** @type {Comment} */ (head_anchor).data !== hash)
		) {
			head_anchor = get_next_sibling(head_anchor);
		}

		// If we can't find an opening hydration marker, skip hydration (this can happen
		// if a framework rendered body but not head content)
		if (head_anchor === null) {
			set_hydrating(false);
		} else {
			var start = /** @type {TemplateNode} */ (get_next_sibling(head_anchor));
			head_anchor.remove(); // in case this component is repeated

			set_hydrate_node(start);
		}
	}

	if (!hydrating) {
		anchor = document.head.appendChild(create_text());
	}

	try {
		block(() => render_fn(anchor), HEAD_EFFECT);
	} finally {
		if (was_hydrating) {
			set_hydrating(true);
			set_hydrate_node(/** @type {TemplateNode} */ (previous_hydrate_node));
		}
	}
}