Why isn't `Promise.all()` overloaded?

# Jacob Pratt (7 days ago)

This is potentially a very simple question, Promise.all() takes a single iterable as a parameter. Is there any particularly reason it wasn't overloaded to allow passing multiple parameters (and use ...arguments)? Of course, the only difference is the creation of an array, but it is an array that doesn't need to be created.

Jacob Pratt

# Tab Atkins Jr. (7 days ago)

On Fri, Aug 10, 2018 at 2:30 PM Jacob Pratt <jhprattdev at gmail.com> wrote:

This is potentially a very simple question, Promise.all() takes a single iterable as a parameter. Is there any particularly reason it wasn't overloaded to allow passing multiple parameters (and use ...arguments)? Of course, the only difference is the creation of an array, but it is an array that doesn't need to be created.

API complexity - Promise.all()'s promise resolves to an array of resolved values. How would multiple input iterables be reflected here? Just concatenated together? More straightforward and predictable to just ask the user to concatenate things on the input side.

Also, Promise.all(), following the example of other promise methods, doesn't require the values in the input array to be promises; it just Promise.resolve()'s all of them, so you can pass in non-Promise values as well. With a "multiple input arguments" API shape, it's less clear that Promise.all("foo", "bar") is wrong, for instance (it would treat each of them as a 3-element array of characters). With the current design you usually have to put in a literal [], so it's easier to remember the API shape.

# Jordan Harband (7 days ago)

In addition to what Tab said, it produces a Promise for an iterable (that happens to be an array), so it makes perfect sense that it takes an iterable of the same number of items, so there's a 1-1 mapping.