5 ms·

Arrow Functions Coming to Chrome 45

34 points by apaprocki 11y ago

homulilly 11y ago
I take it this means we'll also get arrow functions enabled by default in IO.js shortly?
egeozcan 11y ago
Regarding the example at the end of the post, how does it even make sense to allow an anonymous arrow function be a "paramater name" (yes!) of another anonymous function? I guess the empty object becomes a destructuring parameter that doesn't do anything but the function is confusing: ( ( {}, {}, ({},{})=>({},{}) )=> (({},{})=>({},{}),{},{}) )({},{}) I can rewrite that to be more clear: //(({},{})=>({},{}),{},{}) evaluates to {} //({},{}) evaluates to {} let fn = ({}, {}, ({},{})=>{}) => {}; fn({},{}); This is just a syntax error, I guess (hope)?
- SerpentJoe 11y ago
  It is. You can try to translate the snippet using babel, it doesn't work unless you remove that parameter.
0x0 11y ago
Why is it that all new chrome features are usually announced on random blogs all over the place, while the official "chromereleasenotes" blogspot blog has almost never any useful information? There they all seem to talk about various minor security fixes in the stable channel posts, but almost never are new features highlighted. Is it really necessary to track the beta and canary release notes and svn logs to stay on top of things?
- dragonwriter 11y ago
  Because individual devs with "random blogs" know about actions they've taken sooner than its filtered into official corporate announcements. > There they all seem to talk about various minor security fixes in the stable channel posts, but almost never are new features highlighted. Is it really necessary to track the beta and canary release notes and svn logs to stay on top of things? New JS features and the like seem to be announced on the chromium blog (not the chrome releases blog), but often only with Beta releases. 45 hasn't hit Beta yet, so... But the most complete official source of information on feature status isn't a blog, its https://www.chromestatus.com/features https://www.chromestatus.com/features
- owencm 11y ago
  We try and make sure that the Chromium blog (http://blog.chromium.org/ http://blog.chromium.org/) always covers new features as they make it into the new Beta. Imho you should be able to read the beta blog posts on that blog and not miss any new developer shiny things. Also fwiw we're going to try and do a better job of making the release notes link to the appropriate beta blog post on the Chromium blog, I agree we've done a poor job on that in the past.
  - 0x0 11y ago
    Awesome, thanks!
apalmer 11y ago
No Offense, but arrow functions and the 'let' keyword in particular just seem like really bad ideas for javascript.
- aikah 11y ago
  why? i'd say if es6 had only 2 features one should be at least => .
  - apalmer 11y ago
    Arrow functions are worse, as far as I can tell the only benefit is to save a few characters of text. To get this win, now I have to always be conscious of how a function was created which syntax was used and as a result how 'this' was bound. basically it is a 'fix' to a unusual but completely working and simple to reason about programming feature by adding a more correct but very inconsistent with the rest of the language that makes the whole thing harder to reason about. does it serve any other benefit? I might be missing something as many people love this feature.
    - steego 11y ago
      When I'm working with C#, I often write code like so: products .Where(p => p.Price >= range.low && p.Price <= range.high) .GroupBy(p => p.Category) .Select(g => new { Category = g.Key.Name, Count = g.Count() }) It's not just about saving a few characters. It's about about making certain types of libraries readable by reducing the amount of noise.
    - nacs 11y ago
      > does it serve any other benefit Yes, as stated in the linked article: > arrow functions don't define this or arguments in their bodies, instead capturing these values from the environment Also: https://hacks.mozilla.org/2015/06/es6-in-depth-arrow-functions/ https://hacks.mozilla.org/2015/06/es6-in-depth-arrow-functio...
- paublyrne 11y ago
  No offence taken, but what about let do you think is wrong for JavaScript? It will help make common scope errors less common, and is clean to read.
moron4hire 11y ago
> Relative to the other kind of function that is written like function (x) { return x * 2 }, arrow functions don't define this or arguments in their bodies, instead capturing these values from the environment. In the case of `this`, I can see why they did that: it is the right semantics and all of JavaScript should be this way. But I really think creating two different behaviors for what should all just be syntactic sugar around the same, ol' function values is long-term going to reveal itself as a mistake. But that's just `this`. I can't for the life of me imagine why they also did this for `arguments`.
- ubertaco 11y ago
  I think that was largely to make it easier to deal with arrow functions in higher-order functions, though the only case I can see for "arguments" anymore is for varargs, and those are covered with the rest operator, so I'm not sure why the distinction is made.
  - moron4hire 11y ago
    ok, that makes sense. Yes, `arguments` is a shitty replacement for real varargs.
fenomas 11y ago
The author says using arrow functions won't hurt performance, but I wonder if that means v8 knows how to optimize them? Last I checked, using any ES6 syntax causes v8 to permanently deopt the containing function - even using let/const to declare an unused variable that would get removed as dead code. It'll be great once that starts changing..
- chenglou 11y ago
  As of today, Babel turns arrow down to normal anonymous function, and wires up the `this` inside if there's any. So if you compile through Babel (and we'll probably keep compiling for another while) there's no overhead.
  - fenomas 11y ago
    Sure, but that's all true regardless of the Chrome update discussed in the article. That's what I was wondering about.

34 points by apaprocki 11y ago

I take it this means we'll also get arrow functions enabled by default in IO.js shortly?

Regarding the example at the end of the post, how does it even make sense to allow an anonymous arrow function be a "paramater name" (yes!) of another anonymous function? I guess the empty object becomes a destructuring parameter that doesn't do anything but the function is confusing: ( ( {}, {}, ({},{})=>({},{}) )=> (({},{})=>({},{}),{},{}) )({},{}) I can rewrite that to be more clear: //(({},{})=>({},{}),{},{}) evaluates to {} //({},{}) evaluates to {} let fn = ({}, {}, ({},{})=>{}) => {}; fn({},{}); This is just a syntax error, I guess (hope)?

SerpentJoe 11y ago
It is. You can try to translate the snippet using babel, it doesn't work unless you remove that parameter.

0x0 11y ago

Why is it that all new chrome features are usually announced on random blogs all over the place, while the official "chromereleasenotes" blogspot blog has almost never any useful information? There they all seem to talk about various minor security fixes in the stable channel posts, but almost never are new features highlighted. Is it really necessary to track the beta and canary release notes and svn logs to stay on top of things?

dragonwriter 11y ago
Because individual devs with "random blogs" know about actions they've taken sooner than its filtered into official corporate announcements. > There they all seem to talk about various minor security fixes in the stable channel posts, but almost never are new features highlighted. Is it really necessary to track the beta and canary release notes and svn logs to stay on top of things? New JS features and the like seem to be announced on the chromium blog (not the chrome releases blog), but often only with Beta releases. 45 hasn't hit Beta yet, so... But the most complete official source of information on feature status isn't a blog, its https://www.chromestatus.com/features https://www.chromestatus.com/features
owencm 11y ago
We try and make sure that the Chromium blog (http://blog.chromium.org/ http://blog.chromium.org/) always covers new features as they make it into the new Beta. Imho you should be able to read the beta blog posts on that blog and not miss any new developer shiny things. Also fwiw we're going to try and do a better job of making the release notes link to the appropriate beta blog post on the Chromium blog, I agree we've done a poor job on that in the past.
- 0x0 11y ago
  Awesome, thanks!

apalmer 11y ago

No Offense, but arrow functions and the 'let' keyword in particular just seem like really bad ideas for javascript.

aikah 11y ago
why? i'd say if es6 had only 2 features one should be at least => .
- apalmer 11y ago
  Arrow functions are worse, as far as I can tell the only benefit is to save a few characters of text. To get this win, now I have to always be conscious of how a function was created which syntax was used and as a result how 'this' was bound. basically it is a 'fix' to a unusual but completely working and simple to reason about programming feature by adding a more correct but very inconsistent with the rest of the language that makes the whole thing harder to reason about. does it serve any other benefit? I might be missing something as many people love this feature.
  - steego 11y ago
    When I'm working with C#, I often write code like so: products .Where(p => p.Price >= range.low && p.Price <= range.high) .GroupBy(p => p.Category) .Select(g => new { Category = g.Key.Name, Count = g.Count() }) It's not just about saving a few characters. It's about about making certain types of libraries readable by reducing the amount of noise.
  - nacs 11y ago
    > does it serve any other benefit Yes, as stated in the linked article: > arrow functions don't define this or arguments in their bodies, instead capturing these values from the environment Also: https://hacks.mozilla.org/2015/06/es6-in-depth-arrow-functions/ https://hacks.mozilla.org/2015/06/es6-in-depth-arrow-functio...
paublyrne 11y ago
No offence taken, but what about let do you think is wrong for JavaScript? It will help make common scope errors less common, and is clean to read.

moron4hire 11y ago

> Relative to the other kind of function that is written like function (x) { return x * 2 }, arrow functions don't define this or arguments in their bodies, instead capturing these values from the environment. In the case of `this`, I can see why they did that: it is the right semantics and all of JavaScript should be this way. But I really think creating two different behaviors for what should all just be syntactic sugar around the same, ol' function values is long-term going to reveal itself as a mistake. But that's just `this`. I can't for the life of me imagine why they also did this for `arguments`.

ubertaco 11y ago
I think that was largely to make it easier to deal with arrow functions in higher-order functions, though the only case I can see for "arguments" anymore is for varargs, and those are covered with the rest operator, so I'm not sure why the distinction is made.
- moron4hire 11y ago
  ok, that makes sense. Yes, `arguments` is a shitty replacement for real varargs.

fenomas 11y ago

The author says using arrow functions won't hurt performance, but I wonder if that means v8 knows how to optimize them? Last I checked, using any ES6 syntax causes v8 to permanently deopt the containing function - even using let/const to declare an unused variable that would get removed as dead code. It'll be great once that starts changing..

chenglou 11y ago
As of today, Babel turns arrow down to normal anonymous function, and wires up the `this` inside if there's any. So if you compile through Babel (and we'll probably keep compiling for another while) there's no overhead.
- fenomas 11y ago
  Sure, but that's all true regardless of the Chrome update discussed in the article. That's what I was wondering about.