patch function

void patch(Node dom, Morphic prev, Morphic next)

Implementation

void patch(Node dom, Morphic prev, Morphic next) {
  assert(
    _isResolved(prev),
    'prev tree contains unresolved Components. Call resolveNode() first.',
  );
  assert(
    _isResolved(next),
    'next tree contains unresolved Components. Call resolveNode() first.',
  );

  if (prev.runtimeType != next.runtimeType) {
    _replaceAll(dom, prev, next);
    return;
  }

  if (prev is TextMorphic && next is TextMorphic) {
    if (prev.value != next.value) {
      (dom as Text).data = next.value;
    }
    return;
  }

  if (prev is ElementMorphic && next is ElementMorphic) {
    if (prev.tag != next.tag) {
      _replace(dom, createDom(next));
      return;
    }

    final el = dom as Element;
    _patchAttributes(el, prev, next);

    final prevChildren = prev.children.cast<Morphic>();
    final nextChildren = next.children.cast<Morphic>();
    _patchChildren(el, prevChildren, nextChildren);
    return;
  }

  // Fragment → fragment: patch each child in-place via the parent element.
  // The fragment itself has no DOM node — we need its parent to operate on.
  if (prev is FragmentMorphic && next is FragmentMorphic) {
    // Fragment-level patch is handled entirely by _patchChildren of the
    // parent element — fragments expand into their children inline.
    // This branch is only reached if patch() is called directly on a
    // fragment, which should not happen in normal operation.
    return;
  }
}