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Overview of JavaScript ES6 features

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Re: Overview of JavaScript ES6 features

#241

Post by sametmax »

marlonicus wrote: post #227
sametmax wrote: post #203

"you can start using it right now" if you don't care about IE8, IE9, IE10, and many mobile browsers and are willing to ignore 20% of your customers. e.g: http://caniuse.com/#search=let const does not have block scope in those browsers either, but will work, adding to your debugging confusion. template literals and multiline string has no IE support at all (you need edge: https://developer.mozilla.org/en-US/docs/Web/J…

> "20% of your customers" Depends on the product. Regardless, you can easily transpile a codebase to support those browsers. If you aren't doing that already, you probably should be. Otherwise you're supporting a codebase that is quickly going to become very dated and (in comparison to a more modern codebase) much messier.

Yeah but this is not the purpose of the article. The article suggest you don't need to and can use the feature right away. Otherwise it would mentions even mention await, async, yield, etc. and say you can use it too.

Re: Overview of JavaScript ES6 features

#244

Post by z3t4 »

Meegul wrote: post #151
z3t4 wrote: post #143

Earlier quoted context omitted.

> With the asynchronous nature of Javascript, it's theoretically possible for you to declare a variable with `var`, assign it a value, then immediately use that value and find that it's different than what you expected Can you give an example ? My understanding is that the closure freeze the variable in the time the function was called. It can happen if you do not use a closure (function) though.

Here's a post on Stackoverflow that can explain it better than I can: http://stackoverflow.com/questions/21363295/understanding-ja...

Here's how you should do it:

  for(var i=0; i
Or a real world example:

  for(var i=0; i
I've made a blog post about closures: http://www.webtigerteam.com/johan/en/blog/closure_en.htm

It would be cool to write like this (but you cant):

  pattern = texture.map(t => t.onload => ctx.createPattern(t, 'repeat'))

Re: Overview of JavaScript ES6 features

#245

Post by Roboprog »

petersellers wrote: post #219
Meegul wrote: post #130

Earlier quoted context omitted.

It's spelled out pretty well in the article. But if you want another example, consider these two code blocks: var foo; var bar; { let foo = "hello"; var bar = "world"; } console.log(foo); console.log(bar); This produces: undefined world The reason being that the `let` statement restricted that variable to the block it was in (defined by the { and }). `var` declares the variable globally, allowing it to be accessed ou…

"var" declares function scope, not global scope. If you really want global scope, declare the variable with no keyword preceding it (e.g. "foo = 3").

Close. Assigning "foo" without var will look up the lexical scope stack from most nested to global. If nothing exists, it will indeed make a new global. However, if there is a "foo" somewhere in that scope stack, it will update that variable.

    var a = function () {
      var foo
      var b = function () {
        foo = 3
      }
      b()
    }
    a()
    console.log( foo )  // undefined
In the code above, the "foo" in function a is set to 3, rather than creating a global. (changing the "vars" to "lets" would do the same thing, FWIW)

Also, "use strict" mode will not let you make a global that way. If in strict mode, you have to put the "var" outside of any function, then assign it (either on that line, or later) to make a global.

Re: Overview of JavaScript ES6 features

#246

Post by Roboprog »

Meegul wrote: post #130
SHOwnsYou wrote: post #120

Earlier quoted context omitted.

Honest question here --- What is the difference between let and global variables? There are hundreds of articles written about the doom associated with PHP globals, but let appears to be universally lauded. I must be missing something, but I can't tell where.

It's spelled out pretty well in the article. But if you want another example, consider these two code blocks: var foo; var bar; { let foo = "hello"; var bar = "world"; } console.log(foo); console.log(bar); This produces: undefined world The reason being that the `let` statement restricted that variable to the block it was in (defined by the { and }). `var` declares the variable globally, allowing it to be accessed ou…

Javascript (in browser) is async, but not concurrent (like say, threads). JS will run the code in an event handler to completion (or not - while(1){}) before starting the code for the next event. Thus, code from one execution path cannot update variables in another path "immediately".

You could use a variable in a callback for an event that was assigned on the line above, and it since has changed, but it's important to remember that the callback (or promise, etc) does not actually run until an arbitrary time "later".

Re: Overview of JavaScript ES6 features

#247

Post by Roboprog »

z3t4 wrote: post #143
Meegul wrote: post #130

Earlier quoted context omitted.

It's spelled out pretty well in the article. But if you want another example, consider these two code blocks: var foo; var bar; { let foo = "hello"; var bar = "world"; } console.log(foo); console.log(bar); This produces: undefined world The reason being that the `let` statement restricted that variable to the block it was in (defined by the { and }). `var` declares the variable globally, allowing it to be accessed ou…

> With the asynchronous nature of Javascript, it's theoretically possible for you to declare a variable with `var`, assign it a value, then immediately use that value and find that it's different than what you expected Can you give an example ? My understanding is that the closure freeze the variable in the time the function was called. It can happen if you do not use a closure (function) though.

Javascript closures are like Ruby blocks and closures: you get to "touch", as well as "look" - and also see "touches" that happened in between times elsewhere.

Re: Overview of JavaScript ES6 features

#248

Post by mort96 »

oldmanjay wrote: post #105
mort96 wrote: post #61

Earlier quoted context omitted.

This. I personally agree with everyone saying const > let, but I just don't find myself caring enough about it to add the inconvenience of typing 5 characters instead of 3 every time I need to create a variable.

You'd think after all these decades I'd no longer be surprised that programmers try so hard to minimize their typing, since it has no demonstrable positive impact on code quality. I guess premature optimization is in the blood of some people.

It's not about working hard to minimize typing, it's more about not wanting to switch from a state of little typing to a state of more typing. Also, it has nothing to do with optimization; I don't think there exists a single person who uses "let" over "const" because of performance reasons. I also don't think anyone uses "let" over "const" because they think it improves code quality.

Re: Overview of JavaScript ES6 features

#249

Post by Can_Not »

Klathmon wrote: post #232
sametmax wrote: post #223

Earlier quoted context omitted.

It's not what the article is about. The article is obviously talking about native ES6 features, otherwise it would advertise es7 features as well and advise to use transpilers.

There's no reason why someone using babel needs to use ES2016+ features, they can stick to ES2015 just like this article. I'd actually recommend avoiding the still-not-standardized features as you'll have less/no change when it lands in browsers.

I looked at the prospects of starting a React, Aurelia, or VueJS projects a few days ago and a year ago. Anyone who wants to wait to upgrade to these new things will be really happy to see how much nicer these things get every year. Tooling and starter kits just keep getting better, and best of all, you could probably wait a long time to switch and miss out on nothing important.

Re: Overview of JavaScript ES6 features

#250

Post by Can_Not »

abritinthebay wrote: post #225
h1d wrote: post #195

Earlier quoted context omitted.

We have a little more than vi and emacs these days as competition not two sided wars.

Sublime vs Atom if you prefer. The point still stands

Atom is clearly better until you want to open a file larger than 64 bytes.
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