Spread operator doesn't work for arrays

[karelbilek]

This code doesn't typecheck

var a: Array<number> = [1, 2, 3]
var b: Array<number> = [...a];

This is how it works with babel.

Flow just returns

...: rest array of spread operand
This type is incompatible with
....: number

(Spread operator is marked here #560 as done, so I am adding it as a separate issue)

[karelbilek]

This idiom is kinda useless in the simple case, but it is useful in "array-like" objects.

var collection: HTMLCollection = window.document.getElementsByClassName("my-class");
var elements: Array<Element> = [...collection]
//then I can do
elements.filter( /*....something...*/ ).map //...... etc

With Babel REPL.

(Note that this requires Babel polyfill in chrome, because of the use of Array.from.)

[samwgoldman]

Very easy to repro. Seems like a bug to me. Thanks for the report!

[karelbilek]

No problem! I report the bugs as I encounter them in real code :D

[JavascriptMick]

related?

class Person{
  name: string;
  constructor(name){
    this.name = name
  }
}

var map: Map<string, Person> = new Map([
    ['bob', new Person('bob')],
    ['tim',  new Person('tim')],
]);

var count = [...map.values()].filter(p => (p.name=='bob')).length

/Users/michael/Tutorials/node/clickforce_es6/src/Test.js
line 14 col 13 call of method filter - Error:
line 14 col 44 property name - Property cannot be accessed on
line 14 col 17 rest array of spread operand
line 14 col 17 call of method values - Error:
line 14 col 17 Iterator - This type is incompatible with
line 14 col 17 spread operand

[kkirby]

@mdausmann I would guess so.

I just found this bug myself when trying to use it in favor of splice, e.g.: ['abc',...arr]. For others, a workaround would be Array.from as that's what's happening in Babel when you do [...arrayLike].

[jaredly]

still a bug!

[karelbilek]

It works on my copy (at least the current github version)

[gabelevi]

Right, this should be fixed in 0.17.0. 89b5aa6 was the commit that fixed this.

[wldcordeiro]

I can open another issue for this, if you'd like. But from reading into Spread it should work on iterables, so in that case it should work for a Set which is currently an error as of 0.22.0.

[samwgoldman]

@wldcordeiro there is already an open issue for that—on mobile so I can't find it now.

[glortho]

Progress is being made here: #1668