Are ES6 Array comprehensions no longer valid?

Question

The ES6 code snippet below is invalid. It used to be valid. I can still run it in old versions of Traceur but the latest Babel and Traceur don't seem to like the for-loop in an array anymore. Can anyone tell me why it's no longer valid.

let people = [     {         "firstName": "Belinda",         "phone": "1-607-194-5530",         "email": "[email protected]"     },     {         "firstName": "Elizabeth",         "phone": "1-155-446-1624",         "email": "[email protected]"     } ]  let phones = [for({phone} of people) phone]; console.log(phones) 

The snippet below is valid ES6 so I know the destructing inside a for-loop is OK

for(let {phone} of people) {   console.log(phone) } 

Answer 1

Array comprehensions were removed in BabelJS version 6. The ES2015 Specification has no mention of comprehensions, so they were probably dropped. A quick search through the ES Discuss mailing list archives came up empty on anything definitive.

As a slightly more verbose alternative there is Object.entries (a stage-3 feature in ES7) and Array.prototype.map.

let emails = people.map(({ email }) => email); 

Answer 2

http://exploringjs.com/es6/ch_faq.html#_does-es6-have-array-comprehensions is helpful:

Originally, ES6 was to have Array and Generator comprehensions (similarly to Haskell and Python). But they were postponed until after ES6, because TC39 wanted to explore two avenues:

• It may be possible to create comprehensions that work for arbitrary datatypes (think Microsoft’s LINQ).
• It may also be possible that methods for iterators are a better way to achieve what comprehensions do.