Re: [whatwg/dom] Proposal: New method to reorder child nodes (#891)

I'm particularly interested in `parentNode.reorderChildren`, which could probably greatly simplify the reconciliation algorithms in some UI libraries, where reordering (in as few operations as possible) is often the only really "tricky" part. Reconciliation generally adds a lot of complexity - there are many different implementations with many pros and cons, and the code tends to be fairly difficult to understand.

Some concerns/reservations about this feature though:

1. Adding this feature would most likely be a breaking change in terms of `MutationObserver`, which would likely require a new type of mutation? Existing code that currently captures *all* mutations would essentially be incompatible with any newer code that uses the feature - and so, most likely, must be regarded as a breaking change?

2. It probably can't be polyfilled? If you implement a polyfill that uses existing DOM mutations to affect the same change, `MutationObserver` would broadcast these as individual changes.

3. What happens if you pass nodes that aren't already child-nodes of the given parent? Throwing errors of course is one option. Alternatively, this could work like `appendChild` and remove the node from somewhere else, if already present in the document.

4. What happens if you *omit* an existing child-node from the list? Again, throwing errors is an option. More likely, what someone meant to do though, was remove the missing nodes.

(3) and (4) makes me think a method like `setChildren` might be more meaningful - this would clear out nodes no longer in the given list of node, add or move nodes already present in the document, essentially forcing the list of children into a particular state, in a single operation, which is  what most UI libraries are trying to do. This seems more consistent with e.g. `appendChild` and is probably more generally useful? For example, this would make it easy (and fast) to implement sortable table rows.


-- 
You are receiving this because you are subscribed to this thread.
Reply to this email directly or view it on GitHub:
https://github.com/whatwg/dom/issues/891#issuecomment-813040331