Hi! Is there a reason why properties on classes ex...

# javascript

[shama]

Hi! Is there a reason why properties on classes exported to JS are not enumerable? I noticed in 1.4-M1, if I have:

@JsExport
class UIComponent {
    val tagName: String = "h1"
}

It creates the following JS:

function UIComponent() {
  this._tagName = 'h1';
}
UIComponent.prototype._get_tagName_ = function () {
  return this._tagName;
};
Object.defineProperty(UIComponent.prototype, 'tagName', {
  get: UIComponent.prototype._get_tagName_
});

Consuming the JS with: const h1 = new UIComponent(); Object.keys(h1); only gives me the underscore prepended property ["_tagName"]
and for (let p in h1) will enumerate through the _tagName and _get_tagName_ properties but skip over the property I want, tagName.

I was expecting the opposite, where _tagName is not enumerable and tagName is enumerable. The reason is lots of JS libs rely on hasOwnProperty() and being able to enumerate through properties on an object considered its own. My specific use case is Ember.Component.extend(new UIComponent()) doesn’t work because it cannot enumerate and find the properties I have defined.

I think at the very least, enumerable: true should be added to defineProperty() or even better, the public properties get set in the constructor and the behind the scenes ones use defineProperty() and keep the default enumerable: false. But maybe there is a reason they are the way they are. Thanks!

[David Eriksson]

Very interesting case!

[David Eriksson]

The closest thing I can find in the forums is this: https://discuss.kotlinlang.org/t/kotlinjs-object-literals-generate-mangled-names-breaking-hasownproperty/9530

[Sean Keane]

What happens if you annotate the val with @JSExport?

[turansky]

https://youtrack.jetbrains.com/issue/KT-37772

[shama]

Thanks! I’ll watch that issue.

@Sean Keane I tried @JsExport on the val as well as adding open val tagName and both had the same result.