869983 - Class does not seem to work as advertised in the documentation (for FX 20, 21)

Status: RESOLVED WONTFIX

(Add-on SDK Graveyard :: Documentation, defect)

Description

[Mark Goodwin [:mgoodwin]]

I'm trying to use heritage.Class as documented here: https://addons.mozilla.org/en-US/developers/docs/sdk/1.14/modules/sdk/core/heritage.html

My code is here: https://github.com/mozmark/Mitm-Tool/blob/2ff482224c8043d5b06ca7a4bde5cee6147a5b75/lib/config.js#L101

On FX 20 and 21, the properties set via ConfigManager.prototype (e.g. https://github.com/mozmark/Mitm-Tool/blob/2ff482224c8043d5b06ca7a4bde5cee6147a5b75/lib/config.js#L116 ) are undefined when I attempt to use them.

Comment 1

[Matteo Ferretti [:zer0] [:matteo]]

So, the issue here is that in Add-on SDK 1.14, `Class` returns a non extensible constructor, with a non extensible `prototype`. It means that this is working:

    var { Class } = require('sdk/core/heritage');
    var Dog = Class({
      initialize: function initialize(name) {
        this.name = name;
      },
      type: 'dog',
      bark: function bark() {
        return 'Ruff! Ruff!'
      }
    });

But this is not:

    var { Class } = require('sdk/core/heritage');
    var Dog = Class({
      initialize: function initialize(name) {
        this.name = name;
      }
    });

    Dog.prototype.type = 'dog';
    Dog.prototype.bark = function bark() {
        return 'Ruff! Ruff!'
    };

And if the add-on dev is not using "use strict", no exceptions are raised, it will silently fails – properties not added to the prototype.

Probably the misleading part in the documentation was:

> Please note that Class is just an utility function which we use in SDK, and
> recommend our users to use it, but it's in no way enforced. As a matter of fact
> since result is just a plain constructor function with proper prototype chain
> setup

However notice that after 1.14, `Class` returns an extensible constructor and prototype, so also extends the prototype works without issues.

Will, I don't think we need to updated the 1.14 documentation, but what do you think?

Comment 2

[Jeff Griffiths (:canuckistani) (:⚡︎)]

Will, ping?

Comment 3

[Will Bamberg [:wbamberg]]

I don't think it's worth revving the 1.14 documentation for this.

Comment 4

[Matteo Ferretti [:zer0] [:matteo]]

In that case I will set it as "WONTFIX", because the issue is related only for 1.14 documentation.