Add some information about uninitialized class properties #493
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| When invoked via a template `{{user-profile username='example123'}}`, you would expect that `username` would have the value of `example123`, however prior to the native class feature released in Ember `3.6`, this will result in `username` being undefined. |
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We should consider whether it's preferable to just include ember-native-class-polyfill as either a dependency or something we check for in this addon's included() hook. Looks like the polyfill supports at least Ember 3.4 (pzuraq/ember-native-class-polyfill#11) which satisfies our framework version support policy.
The root cause of the problem this documentation is trying to help users avoid, is that babel 7 auto-initializes uninitialized properties to void 0 (possibly for perf reasons, so runtimes see instances as having a consistent shape), which interferes with the way we expect Ember.Component (and Glimmer.Component) to work.
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Initializing the field as void 0 / undefined has the side-effect of being good for perf, but Babel primarily does this to be spec-compliant.
babel/babel#9105 and babel/babel#9141 go into detail about this.
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The polyfill might be the solution for me as I ran into issues with ember upgrade. |
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babel/babel#9105 is not touched upon explicitly here. When a subclass narrows down the type of a property of its superclass, the property is overridden as undefined.
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Got burned by unintialized class properties, which relates to babel/babel#9141