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Overview of JavaScript ES6 features

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Re: Overview of JavaScript ES6 features

#41

Post by djur »

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 should have been "let"/"let mut", not "const"/"let" (or some other scheme that makes immutable bindings terser). I recall people warning of this outcome at the time of standardization.

Re: Overview of JavaScript ES6 features

#42

Post by treehau5 »

chrisseaton wrote: post #28
z3t4 wrote: post #19

var's function scope is a feature! You don't have to place variable declarations in the header! (they are hoisted) Placing the var declarations where they are used makes the code easier to understand. The point of constructor functions is not having to write new . So classes does nothing besides syntactic sugars over the prototype system, witch actually makes it more complicated and the code harder to maintain. Async…

How is having var be function scoped instead of block scoped a useful feature?

Parent literally said why in the rest of their comment. And if you still don't understand why, this probably goes back to understanding JavaScript fundamentals. Not understanding function scope vs block scope is the number one smell for me that someone did not learn JavaScript correctly.

Re: Overview of JavaScript ES6 features

#43

Post by chrisseaton »

treehau5 wrote: post #42
chrisseaton wrote: post #28

Earlier quoted context omitted.

How is having var be function scoped instead of block scoped a useful feature?

Parent literally said why in the rest of their comment. And if you still don't understand why, this probably goes back to understanding JavaScript fundamentals. Not understanding function scope vs block scope is the number one smell for me that someone did not learn JavaScript correctly.

I don't think anything in the rest of their comment has anything to do with block scoping vs function scoping.

I do understand the technical difference very well - I have a PhD in implementing programming languages with function scoping like JavaScript.

If you agree with the person I was replying to maybe could you humour me and explain why you think function-scoping var is a useful feature?

Re: Overview of JavaScript ES6 features

#44

Post by WorldMaker »

z3t4 wrote: post #19

var's function scope is a feature! You don't have to place variable declarations in the header! (they are hoisted) Placing the var declarations where they are used makes the code easier to understand. The point of constructor functions is not having to write new . So classes does nothing besides syntactic sugars over the prototype system, witch actually makes it more complicated and the code harder to maintain. Async…

Arrow functions get auto-named in many browsers based on how they are used. This auto-naming is actually being somewhat standardized between browsers and means there is no difference between anonymous-style function () {} and arrow functions.

Promises are more than just a wrapper around callbacks because they also standardize behavior between "stacks" of callbacks, by instead "chaining" them and creating a standard infrastructure for things like error propagation down a chain. That error propagation and the ability for simple action chaining is worth having over "simple" callbacks, even without the syntactic sugar of async/await.

let/const have similar benefits to function hoisting in that you don't need to declare let/const variables until when you use them. In this case the runtime behavior throws an exception if you try to use them before they are declared (in the so-called hoisting dead zone).

Re: Overview of JavaScript ES6 features

#45

Post by pmoleri »

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…

I resisted const for like 10 minutes. You get used to it really quickly and then when you see a 'let' in your code you just know something is happening with that variable afterwards.

When I have to go back to programming in a language without const declarations it feels bad.

Re: Overview of JavaScript ES6 features

#46

Post by treehau5 »

chrisseaton wrote: post #43
treehau5 wrote: post #42

Earlier quoted context omitted.

Parent literally said why in the rest of their comment. And if you still don't understand why, this probably goes back to understanding JavaScript fundamentals. Not understanding function scope vs block scope is the number one smell for me that someone did not learn JavaScript correctly.

I don't think anything in the rest of their comment has anything to do with block scoping vs function scoping. I do understand the technical difference very well - I have a PhD in implementing programming languages with function scoping like JavaScript. If you agree with the person I was replying to maybe could you humour me and explain why you think function-scoping var is a useful feature?

> I do understand the technical difference very well - I have a PhD in implementing programming languages like JavaScript.

I am happy for your PhD and that it is for implementing programming languages like JavaScript.

My assertion is the advantage of having function scoping is apparent to those who understand function scoping. Block scoping-style programming in JavaScript was always, in my experienced, shoe-horned in by people who wanted to make JavaScript more like Java. That is all there is to my point.

Re: Overview of JavaScript ES6 features

#47

Post by WorldMaker »

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 also doesn't help that let is 3 letters versus const is 5; programmers if anything will default to the faster to type option.

Re: Overview of JavaScript ES6 features

#48

Post by depr »

epmatsw wrote: post #35
z3t4 wrote: post #19

var's function scope is a feature! You don't have to place variable declarations in the header! (they are hoisted) Placing the var declarations where they are used makes the code easier to understand. The point of constructor functions is not having to write new . So classes does nothing besides syntactic sugars over the prototype system, witch actually makes it more complicated and the code harder to maintain. Async…

Promises and callbacks have fundamentally different behavior. Promises are much more reliable (only executed a single time, always executed asynchronously vs possibly synchronously, etc.) and also have slightly different execution behavior in the event loop. People emphasize the syntax differences, but that's not the most useful thing about Promises imo. You Don't Know JS's async book has an excellent in-depth writeu…

The function passed to the promise is executed synchronously, the call to `then` is always asynchronous.

Re: Overview of JavaScript ES6 features

#49

Post by JoeAltmaier »

pmoleri wrote: post #45
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…

I resisted const for like 10 minutes. You get used to it really quickly and then when you see a 'let' in your code you just know something is happening with that variable afterwards. When I have to go back to programming in a language without const declarations it feels bad.

I know I should use const. I lazily leave it until the end then try to shoe-horn it in. Then it ripples through the code until I give up. Then I hate myself.

Re: Overview of JavaScript ES6 features

#50

Post by ggregoire »

jnasc wrote: post #38

What about import from? (modules)

In my opinion it's the biggest improvement from ES6. However, you still need Babel to use this feature, even in Chrome/Firefox.

For those interested:

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

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

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