Is it possible to deepmerge an HTML dom object? about deepmerge

[RebeccaStevens]

Look like the problem you have here is slotElm isn't a "plain object" and deepmerge is using its default cloning under the hood which only handles cloning of "plain objects".

There are 2 easy solutions to fix this.
Either tell deepmerge to not clone by setting the clone option to false,
or tell deepmerge that DOM Objects are not mergeable (/cloneable) by setting the isMergableObject option (see: https://github.com/TehShrike/deepmerge#ismergeableobject - you probably want to use is-plain-object).

[AndrewRedican]

It is unlikely this will be supported. Unless the implementation used symbol to track where the algorithm has traversed.
DOM objects have references to itself this is why you get RangeError, it is likely to be causing infinite recursion at fails after 50 levels of depth or so.

[TehShrike]

Also I believe most DOM elements have internal state that prevents them from being cloned by userland code.

You probably want Node.cloneNode()