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polymerpolymer-1.0observers

How do I set and unset an observer in Polymer?

I'm trying to understand the right way to go about setting and unsetting an observer within a Polymer component within attached() and detached() events, so it only starts watching after the element is attached. Any ideas?

Solution

  • Currently, there is no public API to imperatively add observers (but a private one exists), and no API at all to remove them.

    The private function, _addComplexObserverEffect(...), creates an observer on one or more properties. It's this function that processes each observer expression in the Polymer object's observers array. Note the caveat of using a private function is it could be unusable in the next release.

    You could use it like this:

    Polymer({
  ...,

  properties: {
    foo: String
  },

  attached: function() {
    this._addComplexObserverEffect('_fooChanged(foo)');
  },

  _fooChanged: function(foo) { ... }
});

    codepen