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LibWeb: Don't create mutation record node lists if nobody is interested

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By deferring allocation of StaticNodeList objects until we know somebody
actually wants the MutationRecord, we avoid a *lot* of allocation work.

This shaves several seconds off of loading https://tc39.es/ecma262/

At least one other engine (WebKit) skips creating mutation records if
nobody is interested, so even if this is observable somehow, we would
at least match the behavior of a major engine.
This commit is contained in:
Andreas Kling 2023-05-17 19:47:16 +02:00
parent 0f2b6345c6
commit 80d6330a26
4 changed files with 22 additions and 31 deletions
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4
Userland/Libraries/LibWeb/DOM/Attr.cpp
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@ -89,9 +89,7 @@ void Attr::set_value(DeprecatedString value)
void Attr::handle_attribute_changes(Element& element, DeprecatedString const& old_value, DeprecatedString const& new_value)
{
// 1. Queue a mutation record of "attributes" for element with attribute’s local name, attribute’s namespace, oldValue, « », « », null, and null.
auto added_node_list = StaticNodeList::create(realm(), {}).release_value_but_fixme_should_propagate_errors();
auto removed_node_list = StaticNodeList::create(realm(), {}).release_value_but_fixme_should_propagate_errors();
element.queue_mutation_record(MutationType::attributes, local_name(), namespace_uri(), old_value, added_node_list, removed_node_list, nullptr, nullptr);
element.queue_mutation_record(MutationType::attributes, local_name(), namespace_uri(), old_value, {}, {}, nullptr, nullptr);
// 2. If element is custom, then enqueue a custom element callback reaction with element, callback name "attributeChangedCallback", and an argument list containing attribute’s local name, oldValue, newValue, and attribute’s namespace.
if (element.is_custom()) {