Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Overview of JavaScript ES6 features

adrianmejia.com

Post reply on HN
Print view View original

71–80 of 250 posts

Re: Overview of JavaScript ES6 features

#71

Post by riquito »

ggregoire wrote: post #39

I'm surprised by the state of const/let nowadays. The well-known good practice: use const by default; use let when it's needed. At the release of ES6, it was the way to go. But everyday I notice libraries—and some really famous— that use let everywhere in their docs, or some really influent developers from Google or Facebook who share samples of code on Twitter using let when it's not needed [1]. I don't know why. Se…

It doesn't help that many variables are objects, and const means that you cannot reassign the variable, not that you cannot modify it.

e.g.

    const x = {};
    x.foo = 'it works!'

Re: Overview of JavaScript ES6 features

#72

Post by ggregoire »

fryan wrote: post #65
zelias wrote: post #55

While I'm a big believer in most of the ES6 changes (arrow functions! let/const! classes! generators!), I am not a big fan of many of the new destructuring features. They can actually make your code less approachable if you don't already know what's going on.

I agree that object destructuring makes the code far less readable. Array destructuring however is easy for anyone to grok.

It depends I think.

For example, in my opinion

    const Header = ({ children, iconName, iconSize, title }) => { ... };
is more readable than

    const Header = (props) => { ... };

Re: Overview of JavaScript ES6 features

#73

Post by Roboprog »

zelias wrote: post #55

While I'm a big believer in most of the ES6 changes (arrow functions! let/const! classes! generators!), I am not a big fan of many of the new destructuring features. They can actually make your code less approachable if you don't already know what's going on.

The deep matching gets too cluttered, but the simple case I find to be quite readable and useful:

http://es6-features.org/#ObjectMatchingShorthandNotation

Re: Overview of JavaScript ES6 features

#74

Post by ggregoire »

riquito wrote: post #71
ggregoire wrote: post #39

I'm surprised by the state of const/let nowadays. The well-known good practice: use const by default; use let when it's needed. At the release of ES6, it was the way to go. But everyday I notice libraries—and some really famous— that use let everywhere in their docs, or some really influent developers from Google or Facebook who share samples of code on Twitter using let when it's not needed [1]. I don't know why. Se…

It doesn't help that many variables are objects, and const means that you cannot reassign the variable, not that you cannot modify it. e.g. const x = {}; x.foo = 'it works!'

Maybe in ES9 we will have

    immut x = {};
    x.foo = 'it doesn't work! :)'
At the moment, we can use these libs to achieve it

- https://github.com/rtfeldman/seamless-immutable

- https://github.com/facebook/immutable-js

Re: Overview of JavaScript ES6 features

#75

Post by zbjornson »

riquito wrote: post #71
ggregoire wrote: post #39

I'm surprised by the state of const/let nowadays. The well-known good practice: use const by default; use let when it's needed. At the release of ES6, it was the way to go. But everyday I notice libraries—and some really famous— that use let everywhere in their docs, or some really influent developers from Google or Facebook who share samples of code on Twitter using let when it's not needed [1]. I don't know why. Se…

It doesn't help that many variables are objects, and const means that you cannot reassign the variable, not that you cannot modify it. e.g. const x = {}; x.foo = 'it works!'

This is the same as a const ptr in C: the pointer can't change but the value it points to can. While it may seem broken it has its uses. Doing deep watches to disallow object mutation would be impossibly expensive (I think?).

Re: Overview of JavaScript ES6 features

#77

Post by VeejayRampay »

duckfruit wrote: post #58
VeejayRampay wrote: post #53

I have a question: What does `for element of arr` buy me over `arr.forEach(element => ...)` I don't find the for...of syntax particularly appealing or useful, but I might be missing something. Is it a matter of preference?

for...of is more flexible. While forEach is a method on Array.prototype, for...of is a consistent syntax that can be used in more places. For instance, iterables: function *myIterable (v) { while(--v) yield v } let launchCountdown = myIterable(60) for (let i of launchCountdown) console.log(`t minus ${i} seconds`) So in effect arrays can be thought of as iterables in ES6. So IMHO it allows for more consistent behavior…

Ah, I see, good point. And how would you handle cases (that I end up using quite often) such as :

arr.map(...).filter(...).forEach(...) which allows me to iterate over the filtered result? One would assign the result of filter to a variable and call for...of on that?

EDIT: Also, I never saw any mention of for...of working for object literals (à la `for (let [key, value] of obj`), I suppose that's out of scope, correct?

Re: Overview of JavaScript ES6 features

#78

Post by Roboprog »

Tankenstein wrote: post #5
neximo64 wrote: post #2

Using const and `splice` breaks the rules: const info = [1,2,3,4] const newInfo = info.splice(2); 'info' has changed

Common misconception, const only disallows reassignment. For instance, const number = 1337; number = 10; // fails But objects/arrays are not immutable in js, so you can do this: const person = { name: 'Dude' }; person.name = 'Dudette'; Which is perfectly valid. If you want full immutability, i recommend you check out https://facebook.github.io/immutable-js/ , been running it in production, a real pleasure to work wit…

Any popular "deep freeze" utilities around?

Re: Overview of JavaScript ES6 features

#79

Post by paradite »

riquito wrote: post #71
ggregoire wrote: post #39

I'm surprised by the state of const/let nowadays. The well-known good practice: use const by default; use let when it's needed. At the release of ES6, it was the way to go. But everyday I notice libraries—and some really famous— that use let everywhere in their docs, or some really influent developers from Google or Facebook who share samples of code on Twitter using let when it's not needed [1]. I don't know why. Se…

It doesn't help that many variables are objects, and const means that you cannot reassign the variable, not that you cannot modify it. e.g. const x = {}; x.foo = 'it works!'

Oh I didn't realize that. I assumed that const means immutable.

Now I am going back to change all the object declarations to const.

Re: Overview of JavaScript ES6 features

#80

Post by zbjornson »

fenomas wrote: post #22
my123 wrote: post #7

On the web browser side, I don't recommend using ES6 yet, without any kind of fallback. Internet Explorer 11 is still used, as are devices on older iOS versions. (without counting people using the default browser on pre-Lollipop Android)

Also - for anyone writing code where performance matters, the question isn't when browsers support the syntax, it's when each JS engine's optimizations support it. E.g.: until some months ago just putting "let foo" into a function would cause V8 to bailout (meaning the whole function gets executed slowly, even if the actual let statement gets removed as dead code). Unfortunately I've never found any good references o…

https://docs.google.com/document/d/1EA9EbfnydAmmU_lM8R_uEMQ-...

That's the planning doc for v8 optimization of ES2015+ and an interesting read.

Post reply on HN