Attribute values should be copied to property values before created

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<!DOCTYPE html>
<html>
<head>
<script src="polymer.min.js"></script>
<polymer-element name="my-lifecycle" attributes="foo">
  <script>
    Polymer('my-lifecycle', {
      created: function() {
        console.log('created', this.foo);
      },
      ready: function() {
        console.log('ready', this.foo);
      },
    });
  </script>
</polymer-element>
</head>
<body>
<my-lifecycle foo="bar"></my-lifecycle>
</body>
</html>

produces a console log of:

created null
ready bar

which surprised me, and doesn't seem to be implied by http://www.polymer-project.org/polymer.html#configuring-an-element-via-attributes or http://www.polymer-project.org/polymer.html#lifecyclemethods. This could just be a documentation issue, but created seems like the place to "configure" an element, so it seems like the attributes should be propagated in at this point rather than waiting until ready.

Generally element initialization code should be called from ready. created corresponds to createdCallback from the spec. This is the first callback an element receives and Polymer sets up data binding, property observers, Shadow DOM, etc. for the element at this time, which is why the attributes are not reflected to the properties at created time.

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Attribute values should be copied to property values before `created` #342

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Attribute values should be copied to property values before created #342

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morethanreal commented on Nov 8, 2013

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Attribute values should be copied to property values before `created` #342