Why Map#merge() limited to joining 2 maps?

[bdistin]

It seems when doing joins, currently, the most common behavior is being able to join/merge a virtually unlimited number of other structures.

Examples:

1. Array#push(value1[, value2[, ...[, valueN]]]);
2. Array#unshift(value1[, value2[, ...[, valueN]]]);
3. Array#concat(array1[, array2[, ...[, arrayN]]]);
4. Object.assign(object1[, object2[, ...[, objectN]]]);

Exceptions:

1. Set#add();

Which you are happening to be fixing by adding Set#addAll(). (Side note: In my opinion, it would be better to change the semantics of Set#add() to allow adding several elements, than to add Set#addAll(), if possible)

Why didn't I list Map#set() as an exception? Because Map#set() seems more like an assignment operation, like Object.defineProperty(). Although to be fair, there is enough room for Object.defineProperties() in the lang, so it may be a mistake I separate it. I suppose that's up to interpretation.

For consistent design, I think the proposed Map#merge() should allow: Map#merge(iterator1[, iterator2[, ...[, iteratorN]]]);. What do you think about this?

[zloirock]

Side note: In my opinion, it would be better to change the semantics of Set#add() to allow adding several elements

It will break code like array.forEach(set.add, set) so it's unacceptable.

I think the proposed Map#merge() should allow: Map#merge(iterator1[, iterator2[, ...[, iteratorN]]])

Makes sense.

[bdistin]

Ah, I see what you mean with Set#add(). I will strike that note from the OP.