Overview of JavaScript ES6 features

Post by betenoire » Mon, Oct 24, 2016, 5:04 PM UTC

cloakandswagger wrote: post #86

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…

Is it just me, or is Javascript (and more generally, all front end technology) more susceptible to these trivial holy wars? While I agree that const/let is a useful convention for communicating mutability, it isn't nearly a big enough deal to warrant the attention it receives from the community. It's not just const/let; I rarely make a front end PR that isn't bike-shedded to death over subjective styling choices, sin…

Post by AgentME » Mon, Oct 24, 2016, 5:13 PM UTC

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!'

    let x = {};
    const y = x;
    x.a = 5;

Post by AngeloR » Mon, Oct 24, 2016, 5:16 PM UTC

cloakandswagger wrote: post #86

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…

Is it just me, or is Javascript (and more generally, all front end technology) more susceptible to these trivial holy wars? While I agree that const/let is a useful convention for communicating mutability, it isn't nearly a big enough deal to warrant the attention it receives from the community. It's not just const/let; I rarely make a front end PR that isn't bike-shedded to death over subjective styling choices, sin…

Post by netule » Mon, Oct 24, 2016, 5:19 PM UTC

zbjornson wrote: post #75

riquito wrote: post #71

Earlier quoted context omitted.

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?).

  type const * const

Post by bzbarsky » Mon, Oct 24, 2016, 5:23 PM UTC

VeejayRampay wrote: post #77

duckfruit wrote: post #58

Earlier quoted context omitted.

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, correc…

  for (let [key, value] of Object.entries(obj)) {
  }