8 ms·

ECMAScript 2018 Language Specification

149 points by treyhuffine 9y ago

heydenberk 9y ago
It's not easy to tell from this document what has changed, but Dr. Axel Rauschmayer does a good job here http://2ality.com/2017/02/ecmascript-2018.html http://2ality.com/2017/02/ecmascript-2018.html
- paws 9y ago
  A few paragraphs down, you should find: This specification introduces Async Functions, Shared Memory, and Atomics along with smaller language and library enhancements, bug fixes, and editorial updates. Async functions improve the asynchronous programming experience by providing syntax for promise-returning functions. Shared Memory and Atomics introduce a new memory model that allows multi-agent programs to communicate using atomic operations that ensure a well-defined execution order even on parallel CPUs. This specification also includes new static methods on Object: Object.values, Object.entries, and Object.getOwnPropertyDescriptors.
  - growtofill 9y ago
    Nope, that’s a copy-paste from last year’s spec: http://www.ecma-international.org/publications/files/ECMA-ST/Ecma-262.pdf#page53 http://www.ecma-international.org/publications/files/ECMA-ST...
    - bterlson 9y ago
      I will be writing the ES2018 intro prose around when we send ES2018 draft to ECMA for ratification (few months away yet).
growtofill 9y ago
According to [the repo](https://github.com/tc39/proposals/blob/master/finished-proposals.md https://github.com/tc39/proposals/blob/master/finished-propo...) only one minor feature had reached stage 4 since last year. Not sure why this is on top HN.
- irrational 9y ago
  My understanding is ES2015 was huge, but E2016, ES2017, ES2018, etc. are comparatively tiny.
- gitconnected 9y ago
  A small update is just as important news as a large update. It's a signal about where Javascript stands as a language.
- bterlson 9y ago
  There are many proposals sitting at the cusp of the stage 3 to stage 4 transition. There will be a couple more meaty things to make it. I suspect we'll end up with more proposals ready than I have time to integrate into the main spec :)
xamuel 9y ago
Template Literal Revision [1] is a welcome change, but still falls way short, as there's still no way to easily include the backtick itself inside raw text. I wish ES would adopt python-style triple-quotes, so you could do things like: String.raw```Look, this is a backtick: "`"``` (The inability to do this is a pain point when you want to embed a language in ES and that language itself makes use of backticks.) [1] http://2ality.com/2016/09/template-literal-revision.html http://2ality.com/2016/09/template-literal-revision.html
- mistercow 9y ago
  Can't you just do `Look, this is a backtick: ${'`'}`? Or are you not counting that as "easy" because it's horrible.
  - xamuel 9y ago
    Suppose I wanted to embed your solution itself into a template literal. It would look like this: `${'`'}Look, this is a backtick: \${'${'`'}'}${'`'}`
    - Arnavion 9y ago
      Rust has a nice solution to this. r"foo" == "foo" // r" means the literal ends at " r#""foo""# == "\"foo\"" // r#" means the literal ends at "# r##"r#""foo""#"## == "r#\"\"foo\"\"#" // r##" means the literal ends at "## and so on. Basically you add as many # outside as necessary to distinguish the end of the literal (double-quote followed by some #) from any such sequence in the middle of the literal.
      - analogic 9y ago
        just blue my mind. is there a babel plugin that will let me do this?
    - sterlingfs 9y ago
      Web components are the answer for creating composable templates.
bascule 9y ago
I guess BigInt (i.e. native integer support) is only stage 3: https://github.com/tc39/proposal-bigint https://github.com/tc39/proposal-bigint It's the feature I'd most like to see added.
- ralusek 9y ago
  Didn't even know that was on the docket, that's awesome. Would doing operations on them automatically cast them to float64? I know they offer integer typed arrays, but any mathematical operations will automatically cast them to float64, which is a bummer.
  - nikcub 9y ago
    coercion throws a type error - you can only do ops between bigints
- nikcub 9y ago
  It was only recently bumped up. You can help out by contributing testing etc. in babel[0] or typescript [0] https://github.com/babel/babel/pull/6015 https://github.com/babel/babel/pull/6015
mstade 9y ago
I wish the spec included a more bullet pointy changelog from the previous version, but at least it has this paragraph: This specification introduces Async Functions, Shared Memory, and Atomics along with smaller language and library enhancements, bug fixes, and editorial updates. Async functions improve the asynchronous programming experience by providing syntax for promise-returning functions. Shared Memory and Atomics introduce a new memory model that allows multi-agent programs to communicate using atomic operations that ensure a well-defined execution order even on parallel CPUs. This specification also includes new static methods on Object: Object.values, Object.entries, and Object.getOwnPropertyDescriptors.
- growtofill 9y ago
  That’s ECMAScript 2017.
  - mstade 9y ago
    You're right, thanks for the correction. Very confusing language though, an oversight in editing perhaps?
allenwb 9y ago
That document is an incomplete working DRAFT for the next edition of the ECMAScript standard. Don't assume that the current snapshot is feature complete.
- bterlson 9y ago
  More strongly, the draft is incomplete by its very nature. If you care about having only complete and ratified standards, do not use the GitHub snapshot. Use the official versions hosted on ECMA's website (https://www.ecma-international.org/memento/TC39-M.htm https://www.ecma-international.org/memento/TC39-M.htm).
nikcub 9y ago
Optional catch binding[0], which is at stage 3, seems like a bad idea[1] and has been pointed out as such[2] [0] http://2ality.com/2017/08/optional-catch-binding.html http://2ality.com/2017/08/optional-catch-binding.html [1] http://wiki.c2.com/?EmptyCatchClause http://wiki.c2.com/?EmptyCatchClause [2] https://github.com/tc39/proposal-optional-catch-binding/issues/2 https://github.com/tc39/proposal-optional-catch-binding/issu...
- bterlson 9y ago
  If anyone has any data on this topic I would love to hear and understand it!
- acdha 9y ago
  The github issue seems to cover this well: existing linters have code to cover intentionally unused bindings and this is a cleaner way to express that. Do you disagree with the rationale in that discussion?
  - pitaj 9y ago
    That's true, but in that case adding optional catch binding is completely useless.
  - nikcub 9y ago
    I'd be more ok with it being paired with exception filtering (or what Netscape called conditional catch clauses), ie. } catch (e if e instanceof CriticalError) { // handle critical } catch (e if e instanceof TypeError) { // handle type mismatch } catch () { } so you could at least handle critical and other errors before blindly silencing - but for some reason exception filtering/conditional catch hasn't come up in ECMA
gitconnected 9y ago
Still a working draft, but great to see all the potential updates
sterlingfs 9y ago
Im honestly not trying to be like TLDR, but a revision log would be immensely appreciated.
- bterlson 9y ago
  I hear ya. Once the spec is finalized for the year I produce a change log. I have done so in between versions before but things tend to be menial and/or change a lot and it was a lot of work for not too much gain. Willing to go back on this. You can always watch the commits go in here though: https://github.com/tc39/ecma262/commits/master https://github.com/tc39/ecma262/commits/master.
pc2g4d 9y ago
This page is confusing because it describes itself as ECMAScript 2018 but the features it lists are those I've associated with ECMAScript 2017. Looking at the Github repo, you can see that they changed it from 2017 to 2018 on March 31st: https://github.com/tc39/ecma262/commit/8340bf9a8427ea81bb0d1459471afbcc91d18add#diff-3540caefa502006d8a33cb1385720803 https://github.com/tc39/ecma262/commit/8340bf9a8427ea81bb0d1... So what happened to 2017?
- bterlson 9y ago
  Official standards are moved to ECMA's website. E.g. ES2017 is here: https://www.ecma-international.org/publications/files/ECMA-ST/Ecma-262.pdf https://www.ecma-international.org/publications/files/ECMA-S.... The GitHub site is mostly targeted toward implementers who are always working off the latest draft for new spec or implementation work.
sandstrom 9y ago
I hoped decorators[1] would make it, but seems unlikely (looks like they're still at stage 2). [1] https://github.com/tc39/proposal-unified-class-features https://github.com/tc39/proposal-unified-class-features
- bterlson 9y ago
  Probably not ES2018, but 2019 is looking likelier now thanks in part to excellent work by Daniel Ehrenberg (@littledan).
- javajosh 9y ago
  Having spent a long time with Java I believe I understand the limits of this style of coding; in my considered opinion, composition is almost always better than inheritance. This is true regardless of the type of inheritance, be it prototypal or class-based (in appearance or reality). Therefore, adding features to JS to make class-like inheritance slightly better is not a trade-off I would make, favoring a simpler language over a feature who's use shouldn't be encouraged.
  - always_good 9y ago
    They're talking about this section in particular: https://github.com/tc39/proposal-unified-class-features#decorators https://github.com/tc39/proposal-unified-class-features#deco... Where decorators are sugar for higher order functions, even capable of `Class -> Class` transformation, which makes them much different from Java annotations.
johnsonjo 9y ago
I'm really hoping async iterators [1] will make it to stage 4, but from the github I can't really tell what's holding it back as it has several browsers with implementation (I know that's not the only requirement for stage 4, but it's one of them.) I also noticed it's not on the agenda for the November meeting [2]. I understand there are a lot of features being worked on concurrently so it may not be finished by ES2018, but is there any chance someone could give me an update on what's happening with it. I just think this feature is amazing! And also thanks TC39 for all the great features coming to ECMAScript! [1]: https://github.com/tc39/proposal-async-iteration https://github.com/tc39/proposal-async-iteration [2]: https://github.com/tc39/agendas/blob/master/2017/11.md https://github.com/tc39/agendas/blob/master/2017/11.md
- always_good 9y ago
  Async iterators will be cool. Since Java blocks, you can implement a crawler as a custom iterator that makes API requests / paginates behind the scenes and thus abstracts away the fact that it's making a series of requests since the callsite just iterates over the values as it finds them. Would be nice to have that sort of abstraction in Node.
  - hdhzy 9y ago
    > you can implement a crawler as a custom iterator that makes API requests / paginates behind the scenes and thus abstracts away the fact that it's making a series of requests since the callsite just iterates over the values as it finds them. Yep, that's what I had built when they were announced. I had an API that returned a page and "next" pointer but the iterator just returned next item (promise) and followed next links, for the API consumer it looked like a regular collection. Pretty nice! > Would be nice to have that sort of abstraction in Node. Unfortunately Node APIs will probably always lag behind because it's hard to rewrite everything using Promises...
ryanmarsh 9y ago
From section “4. Overview” ECMAScript is an object-oriented programming language for ... heavy sigh
- always_good 9y ago
  As opposed to what? Prototype-based is a form of OOP: https://en.wikipedia.org/wiki/Prototype-based_programming https://en.wikipedia.org/wiki/Prototype-based_programming And "functional programming language" would be way too fine a point, like calling Ruby an FP language.
  - pitaj 9y ago
    Multi-paradigm
acjohnson55 9y ago
My number 1 wish for JavaScript is that it could become fully expression oriented. There's been talk about `do` blocks, which would modify control structures like `if` to become expressions but I don't think that's gone anywhere.

149 points by treyhuffine 9y ago

It's not easy to tell from this document what has changed, but Dr. Axel Rauschmayer does a good job here http://2ality.com/2017/02/ecmascript-2018.html http://2ality.com/2017/02/ecmascript-2018.html

paws 9y ago
A few paragraphs down, you should find: This specification introduces Async Functions, Shared Memory, and Atomics along with smaller language and library enhancements, bug fixes, and editorial updates. Async functions improve the asynchronous programming experience by providing syntax for promise-returning functions. Shared Memory and Atomics introduce a new memory model that allows multi-agent programs to communicate using atomic operations that ensure a well-defined execution order even on parallel CPUs. This specification also includes new static methods on Object: Object.values, Object.entries, and Object.getOwnPropertyDescriptors.
- growtofill 9y ago
  Nope, that’s a copy-paste from last year’s spec: http://www.ecma-international.org/publications/files/ECMA-ST/Ecma-262.pdf#page53 http://www.ecma-international.org/publications/files/ECMA-ST...
  - bterlson 9y ago
    I will be writing the ES2018 intro prose around when we send ES2018 draft to ECMA for ratification (few months away yet).

growtofill 9y ago

According to [the repo](https://github.com/tc39/proposals/blob/master/finished-proposals.md https://github.com/tc39/proposals/blob/master/finished-propo...) only one minor feature had reached stage 4 since last year. Not sure why this is on top HN.

irrational 9y ago
My understanding is ES2015 was huge, but E2016, ES2017, ES2018, etc. are comparatively tiny.
gitconnected 9y ago
A small update is just as important news as a large update. It's a signal about where Javascript stands as a language.
bterlson 9y ago
There are many proposals sitting at the cusp of the stage 3 to stage 4 transition. There will be a couple more meaty things to make it. I suspect we'll end up with more proposals ready than I have time to integrate into the main spec :)

xamuel 9y ago

Template Literal Revision [1] is a welcome change, but still falls way short, as there's still no way to easily include the backtick itself inside raw text. I wish ES would adopt python-style triple-quotes, so you could do things like: String.raw```Look, this is a backtick: "`"``` (The inability to do this is a pain point when you want to embed a language in ES and that language itself makes use of backticks.) [1] http://2ality.com/2016/09/template-literal-revision.html http://2ality.com/2016/09/template-literal-revision.html

mistercow 9y ago
Can't you just do `Look, this is a backtick: ${'`'}`? Or are you not counting that as "easy" because it's horrible.
- xamuel 9y ago
  Suppose I wanted to embed your solution itself into a template literal. It would look like this: `${'`'}Look, this is a backtick: \${'${'`'}'}${'`'}`
  - Arnavion 9y ago
    Rust has a nice solution to this. r"foo" == "foo" // r" means the literal ends at " r#""foo""# == "\"foo\"" // r#" means the literal ends at "# r##"r#""foo""#"## == "r#\"\"foo\"\"#" // r##" means the literal ends at "## and so on. Basically you add as many # outside as necessary to distinguish the end of the literal (double-quote followed by some #) from any such sequence in the middle of the literal.
    - analogic 9y ago
      just blue my mind. is there a babel plugin that will let me do this?
  - sterlingfs 9y ago
    Web components are the answer for creating composable templates.

bascule 9y ago

I guess BigInt (i.e. native integer support) is only stage 3: https://github.com/tc39/proposal-bigint https://github.com/tc39/proposal-bigint It's the feature I'd most like to see added.

ralusek 9y ago
Didn't even know that was on the docket, that's awesome. Would doing operations on them automatically cast them to float64? I know they offer integer typed arrays, but any mathematical operations will automatically cast them to float64, which is a bummer.
- nikcub 9y ago
  coercion throws a type error - you can only do ops between bigints
nikcub 9y ago
It was only recently bumped up. You can help out by contributing testing etc. in babel[0] or typescript [0] https://github.com/babel/babel/pull/6015 https://github.com/babel/babel/pull/6015

mstade 9y ago

I wish the spec included a more bullet pointy changelog from the previous version, but at least it has this paragraph: This specification introduces Async Functions, Shared Memory, and Atomics along with smaller language and library enhancements, bug fixes, and editorial updates. Async functions improve the asynchronous programming experience by providing syntax for promise-returning functions. Shared Memory and Atomics introduce a new memory model that allows multi-agent programs to communicate using atomic operations that ensure a well-defined execution order even on parallel CPUs. This specification also includes new static methods on Object: Object.values, Object.entries, and Object.getOwnPropertyDescriptors.

growtofill 9y ago
That’s ECMAScript 2017.
- mstade 9y ago
  You're right, thanks for the correction. Very confusing language though, an oversight in editing perhaps?

allenwb 9y ago

That document is an incomplete working DRAFT for the next edition of the ECMAScript standard. Don't assume that the current snapshot is feature complete.

bterlson 9y ago
More strongly, the draft is incomplete by its very nature. If you care about having only complete and ratified standards, do not use the GitHub snapshot. Use the official versions hosted on ECMA's website (https://www.ecma-international.org/memento/TC39-M.htm https://www.ecma-international.org/memento/TC39-M.htm).

nikcub 9y ago

Optional catch binding[0], which is at stage 3, seems like a bad idea[1] and has been pointed out as such[2] [0] http://2ality.com/2017/08/optional-catch-binding.html http://2ality.com/2017/08/optional-catch-binding.html [1] http://wiki.c2.com/?EmptyCatchClause http://wiki.c2.com/?EmptyCatchClause [2] https://github.com/tc39/proposal-optional-catch-binding/issues/2 https://github.com/tc39/proposal-optional-catch-binding/issu...

bterlson 9y ago
If anyone has any data on this topic I would love to hear and understand it!
acdha 9y ago
The github issue seems to cover this well: existing linters have code to cover intentionally unused bindings and this is a cleaner way to express that. Do you disagree with the rationale in that discussion?
- pitaj 9y ago
  That's true, but in that case adding optional catch binding is completely useless.
- nikcub 9y ago
  I'd be more ok with it being paired with exception filtering (or what Netscape called conditional catch clauses), ie. } catch (e if e instanceof CriticalError) { // handle critical } catch (e if e instanceof TypeError) { // handle type mismatch } catch () { } so you could at least handle critical and other errors before blindly silencing - but for some reason exception filtering/conditional catch hasn't come up in ECMA

gitconnected 9y ago

Still a working draft, but great to see all the potential updates

sterlingfs 9y ago

Im honestly not trying to be like TLDR, but a revision log would be immensely appreciated.

bterlson 9y ago
I hear ya. Once the spec is finalized for the year I produce a change log. I have done so in between versions before but things tend to be menial and/or change a lot and it was a lot of work for not too much gain. Willing to go back on this. You can always watch the commits go in here though: https://github.com/tc39/ecma262/commits/master https://github.com/tc39/ecma262/commits/master.

pc2g4d 9y ago

This page is confusing because it describes itself as ECMAScript 2018 but the features it lists are those I've associated with ECMAScript 2017. Looking at the Github repo, you can see that they changed it from 2017 to 2018 on March 31st: https://github.com/tc39/ecma262/commit/8340bf9a8427ea81bb0d1459471afbcc91d18add#diff-3540caefa502006d8a33cb1385720803 https://github.com/tc39/ecma262/commit/8340bf9a8427ea81bb0d1... So what happened to 2017?

bterlson 9y ago
Official standards are moved to ECMA's website. E.g. ES2017 is here: https://www.ecma-international.org/publications/files/ECMA-ST/Ecma-262.pdf https://www.ecma-international.org/publications/files/ECMA-S.... The GitHub site is mostly targeted toward implementers who are always working off the latest draft for new spec or implementation work.

sandstrom 9y ago

I hoped decorators[1] would make it, but seems unlikely (looks like they're still at stage 2). [1] https://github.com/tc39/proposal-unified-class-features https://github.com/tc39/proposal-unified-class-features

bterlson 9y ago
Probably not ES2018, but 2019 is looking likelier now thanks in part to excellent work by Daniel Ehrenberg (@littledan).
javajosh 9y ago
Having spent a long time with Java I believe I understand the limits of this style of coding; in my considered opinion, composition is almost always better than inheritance. This is true regardless of the type of inheritance, be it prototypal or class-based (in appearance or reality). Therefore, adding features to JS to make class-like inheritance slightly better is not a trade-off I would make, favoring a simpler language over a feature who's use shouldn't be encouraged.
- always_good 9y ago
  They're talking about this section in particular: https://github.com/tc39/proposal-unified-class-features#decorators https://github.com/tc39/proposal-unified-class-features#deco... Where decorators are sugar for higher order functions, even capable of `Class -> Class` transformation, which makes them much different from Java annotations.

johnsonjo 9y ago

I'm really hoping async iterators [1] will make it to stage 4, but from the github I can't really tell what's holding it back as it has several browsers with implementation (I know that's not the only requirement for stage 4, but it's one of them.) I also noticed it's not on the agenda for the November meeting [2]. I understand there are a lot of features being worked on concurrently so it may not be finished by ES2018, but is there any chance someone could give me an update on what's happening with it. I just think this feature is amazing! And also thanks TC39 for all the great features coming to ECMAScript! [1]: https://github.com/tc39/proposal-async-iteration https://github.com/tc39/proposal-async-iteration [2]: https://github.com/tc39/agendas/blob/master/2017/11.md https://github.com/tc39/agendas/blob/master/2017/11.md

always_good 9y ago
Async iterators will be cool. Since Java blocks, you can implement a crawler as a custom iterator that makes API requests / paginates behind the scenes and thus abstracts away the fact that it's making a series of requests since the callsite just iterates over the values as it finds them. Would be nice to have that sort of abstraction in Node.
- hdhzy 9y ago
  > you can implement a crawler as a custom iterator that makes API requests / paginates behind the scenes and thus abstracts away the fact that it's making a series of requests since the callsite just iterates over the values as it finds them. Yep, that's what I had built when they were announced. I had an API that returned a page and "next" pointer but the iterator just returned next item (promise) and followed next links, for the API consumer it looked like a regular collection. Pretty nice! > Would be nice to have that sort of abstraction in Node. Unfortunately Node APIs will probably always lag behind because it's hard to rewrite everything using Promises...

ryanmarsh 9y ago

From section “4. Overview” ECMAScript is an object-oriented programming language for ... heavy sigh

always_good 9y ago
As opposed to what? Prototype-based is a form of OOP: https://en.wikipedia.org/wiki/Prototype-based_programming https://en.wikipedia.org/wiki/Prototype-based_programming And "functional programming language" would be way too fine a point, like calling Ruby an FP language.
- pitaj 9y ago
  Multi-paradigm

acjohnson55 9y ago

My number 1 wish for JavaScript is that it could become fully expression oriented. There's been talk about `do` blocks, which would modify control structures like `if` to become expressions but I don't think that's gone anywhere.