How to make a class in ecma6 within an encapsulation?

Question

In ecma6 javascript, how can I make a class that is only defined in a scope of something like:

var name_space = new function() {

    class ball {
      ....
    }

    var handball = new ball();  // real object

};

var handball = new ball(); // error, ball not defined

is this possible?

Thanks

It's not clear what you're asking. Can you provide an example use case? — Damon, Jan 17 '17 at 22:05
I tried it and I got an error for the last line. So isn't it already doing what you want? — Barmar, Jan 17 '17 at 22:09
It is pseudo code, i am trying to encapsulate a class definition. — omega, Jan 17 '17 at 22:19
I took out the `....` and ran it in the browser console, it did exactly what you wanted. — Barmar, Jan 17 '17 at 22:22
[**Never** use `new function() {…}`!](http://stackoverflow.com/a/10406585/1048572) — Bergi, Jan 17 '17 at 22:59
Well it will get the new function instance, but it's value is not the point of the question. — omega, Jan 17 '17 at 22:59

score 3 · Accepted Answer · answered Jan 17 '17 at 22:09

3

Sure:

(() => {
  class Ball {

  }

  let handball = new Ball(); // works
})();

let handball = new Ball(); // ReferenceError

You probably don't want to do this, though. ES6 modules are a pleasant alternative to the IIFE pattern.

answered Jan 17 '17 at 22:09

Are you saying that in es6, having global namespaces doesn't work if you do import? – omega Jan 17 '17 at 22:21
1

Basically, yeah. Each module has its own scope, which doesn't pollute the global namespace. You can selectively `export` things from your modules and then pull in only the things you need with `import`. It's the same thing immediately-invoked functions were used to accomplish, just without the clunky syntax. – Jan 17 '17 at 22:53
but if file imports like this `import foo from A', and foo is a function that alerts 1, is it the same thing as var foo = function() {alert(1)}; instead of doing the import? So foo is not in the window variable. – omega Jan 18 '17 at 00:38
I may be misunderstanding your question, so sorry if this isn't what you're getting at but: When you use import and export, each file is a module and each module has its own scope. So when you import `foo` from `A`, it's only available in that file and doesn't get attached to `window` or leak into any other scope. Under the hood, most module bundlers (like Browserify or Webpack) will use functions to wrap everything up and make the code work in a web browser where modules aren't currently supported. Which is a long way to say yeah, foo is not in the window variable. Hope that helps! – Jan 18 '17 at 01:32

score 2 · Answer 2 · answered Jan 17 '17 at 23:08

2

Classes already are defined only in the nearest block scope:

{ // a block scope
    class Ball {
        …
    }
    let handball = new Ball();  // real object
}

var handball = new Ball(); // ReferenceError, Ball not defined

answered Jan 17 '17 at 23:08

Bergi

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How to make a class in ecma6 within an encapsulation?

2 Answers2