[0.8] - default property values are not set by the time observers are called

[ebidel]

In this example, I'm seeing this.published === undefined in keyChanged. I'd expect all of the element's properties to have their default values by the time keyChanged is called:

Polymer({
    is: 'google-sheets',
    properties: {
      key: {
        type: String,
        value: '',
        observer: 'keyChanged'
      },
      published: {
        type: Boolean,
        value: false
      }
    },

    keyChanged: function(newValue, oldValue) {
      //this.published === undefined when the element loads
    }
});

[sorvell]

You cannot depend on the value of one property in the observer of another. Instead consider this:

observers: {
  'key published': 'doStuff'
}

[ebidel]

Thanks @sorvell. So is this the recommended pattern now? I also want to react to individual properties changing later on.

@arthurevans I think we can be more precise in the section on observers. What's not clear:

1. When does the callback get called? end of micro task?
2. If any of the properties change, the callback gets called. People could think they all have to change.

[sorvell]

So is this
https://github.com/Polymer/core-ajax/blob/0.8-preview/core-ajax.html#L308-L311 the
recommended pattern now?

Yes, but this is an area we're still refining so it may change slightly in
the 0.9 timeframe.

When does the callback get called? end of micro task?

Yes

If any of the properties change, the callback gets called. People could
think they all have to change.

Yes

On Sun, Apr 5, 2015 at 9:40 AM, Eric Bidelman [email protected]
wrote:

Thanks @sorvell https://github.com/sorvell. So is this
https://github.com/Polymer/core-ajax/blob/0.8-preview/core-ajax.html#L308-L311
the recommended pattern now? I also want to react to individual properties
changing later on.

@arthurevans https://github.com/arthurevans I think we can be more
precise in the section on observers
https://www.polymer-project.org/0.8/docs/devguide/properties.html#observing-changes-to-multiple-properties.
What's not clear:

1. When does the callback get called? end of micro task?
2. If any of the properties change, the callback gets called. People
   could think they all have to change.

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