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What’s New in ES2019

blog.tildeloop.com

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Re: What’s New in ES2019

#121

Post by snek »

mmartinson wrote: post #101

Honest question, not meant to be inflammatory. If we still need to target es5 4 years later, and transpilation is standard practice, why bother? Is the evolution of JS not directed in practice by the authors of Babel and Typescript? If no one can confidently ship this stuff for years after, what’s the incentive to even bother thinking about what is official vs a Babel supported proposal. I like the idea of idiomatic…

You only need to target old es if you're deploying a website for a big company. Most people don't need IE6 compat. For example, people writing node apps can choose which version of node they deploy.

Re: What’s New in ES2019

#122

Post by coldtea »

mmartinson wrote: post #101

Honest question, not meant to be inflammatory. If we still need to target es5 4 years later, and transpilation is standard practice, why bother? Is the evolution of JS not directed in practice by the authors of Babel and Typescript? If no one can confidently ship this stuff for years after, what’s the incentive to even bother thinking about what is official vs a Babel supported proposal. I like the idea of idiomatic…

>If we still need to target es5 4 years later, and transpilation is standard practice, why bother? Is the evolution of JS not directed in practice by the authors of Babel and Typescript? If no one can confidently ship this stuff for years after, what’s the incentive to even bother thinking about what is official vs a Babel supported proposal.

For one, not everyone works on the client. I can write for Node and use everything v8 supports without ever touching Babel and Typescript.

>I like the idea of idiomatic JS with powerful modern features, but in practice every project I’ve seen seems to use a pretty arbitrary subset of the language, with different ideas about best practices and what the good parts are.

Good parts/best practices are orthogonal to native features and libs, which is what we're discussing here.

Re: What’s New in ES2019

#123

Post by jacobwilliamroy »

addicted wrote: post #117
heavenlyblue wrote: post #21

Earlier quoted context omitted.

I still don't understand why neither JSs var or let allow you to redefine the variable with the same name. I makes chaining things while debugging so much harder: let a = a.project(); let a = debug(a); let a = a.eject(); vs let a1 = a.project(); let a1d = debug(a1); let a2 = a1d.eject();

Without getting into the merits of allowing redefines in a loosely typed language, the simple reason why JS can't support this is hoisting. Any var/let statement of the form var a = 1; is interpreted as 2 statements. (1) The declaration of the variable which is hoisted to the beginning of the variable scope, and the (2) setting of the value, which is done at the location the var statement is at. Having multiple let s…

This human gets it. I'd like to add that if you would like to be clear about what your assignment is doing, put some comments in there.

Re: What’s New in ES2019

#124

Post by snek »

robocat wrote: post #44
alexlur wrote: post #35

That Function.prototype.toString change is probably going to break some Angular.js code who relies on scanning function argument names for dependency injection.

It also requires that comments get stored and waste memory: previously just enough of the AST needed to be stored to be able to regenerate the JavaScript. You can't throw away the comments because you can't predict where code might do someVarHoldingAFunc.toString() It seems like an unnecessary change - if the source needs to be accessed then get the source file.

Engines hold the entire source anyway, with the exception of XS, which returns "[native function]" for everything.

Re: What’s New in ES2019

#125

Post by soulofmischief »

masklinn wrote: post #84
ahmedfromtunis wrote: post #66

Can someone please point me to the rationale behind the new toString() function?

Rather than how complete it is, the real improvements of the proposal are: 1. it all but requires that ES-defined functions stringify to their source code. Pre-ES2019 that's implementation-defined 2. it standardises the placeholder for the case where toString can't or won't create ECMAScript code (e.g. host functions), this could otherwise be an issue as with implementation-defined placeholders subsequent updates to…

Ok that makes sense... I was really confused because that's already more or less toString()'s behavior on modern browsers, though the whitespace discrepancy is important to define.

Re: What’s New in ES2019

#126

Post by masklinn »

vmasto wrote: post #54
jeffwass wrote: post #17

Object.fromEntries will be super useful, surprised it’s taken this long to become a native feature.

What would some common/helpful use cases be?

Functional transformation of objects. There are lots of HOFs working on arrays / iterators but none working on object. fromEntries allows easily converting from object to entries, manipulating the entries sequence and converting back to an object.

The last step is pretty annoying without it.

The entire thing is very common in Python, where Object.entries() is spelled `.items()` and `Object.fromEntries(…)` is spelled `dict(…)`

Re: What’s New in ES2019

#128

Post by masklinn »

steenreem wrote: post #41
NKCSS wrote: post #38

Why did they create a flatMap method? What is wrong with .map(...).flat()? Can they improve the performance by combining it that much?

They could have also implemented flat in terms of flatMap: flatMap(x => x) I personally feel flatMap is a much more used method than flat, so if you want to remove one, I would remove flat.

> They could have also implemented flat in terms of flatMap: flatMap(x => x)

Flat can flatten any level of nesting (it just defaults to 1), so would be difficult to implement in terms of flatMap.

Re: What’s New in ES2019

#129

Post by dsego »

Accacin wrote: post #115
dsego wrote: post #99

Earlier quoted context omitted.

Honest question, not playing. What is exactly exciting about it? 2020 is around the corner and the language created back in 1995 is only now getting features that have been standard in many other languages, either as part of the core language or the standard library for decades.

Well, I'd think that was pretty obvious, right? It's exciting because if you spend the day writing JavaScript I don't give a hoot that another language has had that feature for decades because I don't get to use that other language. Are you implying that no other languages ever add features that other languages have? All languages except JS are feature complete? Come on..

Well now, having an option to use other languages to script web pages, that would be exciting.

Re: What’s New in ES2019

#130

Post by ulisesrmzroche »

stevenmays wrote: post #112
rglover wrote: post #78

That array.flat() and array.flatMap() stuff is great to see. Always having to rely on lodash and friends to do that type of work. Exciting to see how JS is evolving.

I dig it too, but you could previously flatten an array with concat, and the spread operator. [].concat(...array) Lodash wasn't necessary.

Yeah but that reads so gross. Look at it. It’s actually painful.

Much rather have the magic word “flat”

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