Implement arrow functions in v8

https://code.google.com/p/v8/issues/detail?id=2700#c45

by inglor • 11 years ago

44 56 11 years ago

code.google.com

feld3• 11 years ago

Do we just link to random commits now? I have no idea what arrow functions are or why it would even matter to half the people who visit this site.

edit: after following 4 links I finally found the bug report about it

https://code.google.com/p/v8/issues/detail?id=2700

rubiquity• 11 years ago

Then it seems like the perfect opportunity for you to learn something new and stretch your mind a little.

JeremyBanks• 11 years ago

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe...

bsimpson• 11 years ago

Arrow functions are one of the improvements from JS Harmony (which was ratified last night).

This commit moves them from "behind the experimental flag" to "shipping by default" in Chromium. It's a pretty big deal to people who write JS for a living.

feld3• 11 years ago

that's what the synopsis of the post should have been, thanks

towelguy2• 11 years ago

They are a compact way to write anonymous functions in Javascript, so instead of

    var square = function (a) { return a * a;}

You can write:

    var square = a => a * a;

eueueu5• 11 years ago

So basically, a useless hipster fashion lead fluffy syntax change, which mainly makes code harder to read, and makes typos more common.

  // foo takes a function, and a boolean.
  // foo(a=>7, a>=2);

Really? That's easy to read is it? Eugh count me out.

gloriousduke• 11 years ago

Using arrow functions also lexically binds the this value in the anonymous function, an important change for many.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe...

teraflop• 11 years ago

Your link goes to the same page as this post. Was it changed at some point?

feld3• 11 years ago

must have, because it was going directly to the commit which didn't have any useful information.

realusername2• 11 years ago

I'm glad it's finally arriving, it been working in Firefox for quite a long time and I'm happy to see v8 implementing this ! Arrow functions are so much nicer to read and use.

eueueu5• 11 years ago

  a=>b<=7
  a>=b<=7

Can you not see the typos possible with this? The less characters you use for something, the more error prone. There's a reason we don't write in regular expression syntax.

Maybe I'm just getting old!

jahewson2• 11 years ago

Because writing:

    var self = this;
    foo(function(x) {
      return x + self.y;
    });

rather than:

    foo(x => x + this.y)

is so much less error-prone?

danbruc2• 11 years ago

What the heck is the second one supposed to mean? At first it looks a bit like low <= x <= high but with one comparison operator in the wrong direction. I guess it will first compare a and b evaluating to a boolean value, then implicitly convert this result to an integer and finally compare that to 7 again yielding a boolean value. If you write code like that confusion with the arrow notation is one of your smaller problems.

EDIT: Now I got your point - you could accidentally assign a boolean value to a variable when you intended to create a function. One word - compile time type checking. Okay, four, Übersetzungszeittypprüfung in German.

AshleysBrain• 11 years ago

Who on earth would really write that? Surely you'd use the optional braces to make it clearer:

    a => { return b <= 7; }

Sure you can write it without that, but only if you want to write willfully unclear code to annoy people, like writing an entire function body on one line. Just because you can do that doesn't mean that functions are inherently unclear.

astrodust3• 11 years ago

Spend a half decade writing Perl and you'll develop an eye for minute details like that.

People aren't kidding when they say Perl looks like line noise, but you get used to it and can find your way through even a dizzying regular expression with relative ease over time.

Yes, $s=~s+s+S+s+$s is valid Perl.

realusername2• 11 years ago

mmmm, I haven't considered this case... I personally preferred the Coffeescript version like this: a->b<=7 which even without spaces is clearer but maybe they had something incompatible with it.

rimunroe3• 11 years ago

This is a very wrong way of reasoning about probability. The chance that a coin will at some point land on heads does not decrease with the number of flips.

malandrew3• 11 years ago

Do the stack traces for native arrow functions show up in the stack trace as anonymous functions or is only the parent function registered in the stack trace.

davexunit• 11 years ago

Now read the blog post about it! Andy Wingo is a great compiler hacker and he writes about a lot of things that he works on. http://wingolog.org/archives/2015/06/18/arrow-functions-comi...

malandrew3• 11 years ago

Totally agree. Wingolog is an amazing blog and anyone curious about compilers and v8 in general should check it out.

nawitus• 11 years ago

Hmm, I get a syntax error from the puzzle in Firefox.

malandrew3• 11 years ago

Anyone have any idea when destructuring assignment is going to make it into v8?

That is one of the features my colleagues most cite as justification for using babel.js (I wouldn't mind destructuring assigment either). I would love to be able to avoid transpilation since it adds overhead from making out our toolchain more complex and makes debugging more difficult because stack traces and line numbers don't necessarily match up.

cozuya• 11 years ago

On the front end you can get babel to work with sourcemaps fairly easily depending on what build tool you use.

bnoordhuis• 11 years ago

It's in the works: https://code.google.com/p/v8/issues/detail?id=811

You can tell by the number of CLs that a lot of work has been done already but there are a few more still in progress. It's probably still a few weeks out.

Disclaimer: I don't speak for the V8 team, I'm just an interested onlooker.

z3t43• 11 years ago

If you use an anonymous function instead of a named function you'll probably end up writing a comment to clarify ... :P

Sometimes the code explains itself though!?

  allowed = members.filter(member => member.age >= ageLimit);

awalGarg• 11 years ago

It has been reverted[1] now. History repeats itself.

[1] https://code.google.com/p/v8/issues/detail?id=2700#c47

Implement arrow functions in v8

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