Callbacks and extends

[Julien Eluard]

Hi,

testing the 'extends' feature I was surprised to see that callbacks from super elements are not called when overridden. Super callbacks are called when no overrides are provided. Note that calling this.super() does what is expected (see here: http://jsfiddle.net/29btP/)

I had a similar behavior when testing directly with Custom Element.

Is that expected? I find it a little counterintuitive.

Thanks,

Julien

[Scott Miles]

> callbacks from super elements are not called when overridden

This is normal for JavaScript inheritance chains. Any method (including callbacks) resolves to the most-derived (subclass) implementation. The subclass gets the choice of when/how/if to call a superclass method.

I.e., if x-foo has a method 'doStuff', and x-bar extends x-foo, then x-bar can override doStuff and:

• completely redefine doStuff behavior by reimplementing and never calling x-foo.prototype.doStuff
• do some work, then call this.super() to get the default behavior, then do more work
• capture the return value of this.super() and modify or act on it
• control arguments sent to x-foo implementation via this.super() (note that super takes an _array_ of pass-through arguments as a parameter, e.g. `this.super(arguments)` or `this.super([a, 3, null]))

If you automate calling super-class methods, you lose all the flexibility above. This is why we jump through several hoops to provide `this.super` method.

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[Julien Eluard]

Thanks!

I was assuming callbacks would get some special treatment, especially 'created'.

Now it certainly makes sense to provide some flexibility to the user.

Julien