(core) auto-bind this in class-level methods

[anotherchrisberry]

Throwing this out there for discussion.

Much as I love how clean class-level methods are, they don't behave well when called as a result of a promise, e.g.

class Foo {
  this.bar = 3;
  baz() {
    console.log(this.bar)
  }
}
...
let foo = new Foo();
somePromise().then(foo.baz); // throws an exception: "cannot read property 'baz' of undefined"

There are a couple of ways to get around this:

// (1) Invoke via anonymous function
somePromise().then(() => foo.baz());

or

// (2) Declare method using arrow function, binding 'this' to the class instance
class Foo {
  this.bar = 3;
  public baz = () => {
    console.log(this.bar);
}
let foo = new Foo();
somePromise().then(foo.baz); // logs "3"

Preferences on (1) vs. (2)? I prefer (2): it's less surprising to me. But if we go with (2), I'd prefer we declare all class-level methods this way - even those that likely won't be called via a promise, or those that don't reference this in their body.

I'm not opposed to (1), and not in love with (2).

@zanthrash @icfantv @danielpeach what are your thoughts on this? Is there a better, third (or fourth) way around this?

[danielpeach]

What about something like this:
https://github.com/andreypopp/autobind-decorator

[icfantv]

2 feels "wrong" to me only in that it's not a natural way to write class methods. and like all the other solutions, it's a band-aid to get around an annoying limitation...but i don't have anything better to offer here yet.

1 is also annoying, but feels cleaner.

[anotherchrisberry]

Looks like @danielpeach was correct, but will probably use https://github.com/jayphelps/core-decorators.js as it seems to have good support for Typescript and some other nice decorators

[icfantv]

@anotherchrisberry just a heads up: jayphelps/core-decorators#86

[anotherchrisberry]

Going to hold off on the @autobind decorator for now, since it doesn't look like it works with Typescript 2. We are using 1.8 right now but expect to move to 2 this week as we incorporate Angular 2.

We'll revisit this in a few weeks or so. In the meantime, just be aware of this little gotcha.