title: How to use properties declared as Function
body: <p>Polymer has the type <em>Function</em> for its properties (see doc <a href="https://www.polymer-project.org/1.0/docs/devguide/properties" rel="nofollow">here</a>). Do you have any example of its use? Is it possible to pass such function within the html attribute of the tag (e.g., <code>&lt;tagcomponent myfunc="xyz"&gt;</code>)?</p>
  
  <p>I created a polymer components <a href="https://github.com/donpir/polywc-data-table/blob/e6b4581dd2836a3cfdfb85e09753a84fae698228/polywc-data-source-rest.html" rel="nofollow">polywc-data-source-rest</a> to access a restful service using pagination. It has properties to specify the maximum items per page, the page or item offset as in the following snippet of code.</p>
  
  <pre><code>&lt;polywc-data-table&gt;
  &lt;polywc-data-source-rest id="ds"
              base-url="https://data.dublinked.ie/api/action/datastore_search?resource_id=c0ad65f7-6000-4e0d-b972-275cf76d288b"
              items-per-page-key="limit" item-offset-key="offset" 
              post-process-data="fncPostProcessData"&gt;
  &lt;/polywc-data-source-rest&gt;
  &lt;/polywc-data-table&gt;
  </code></pre>
  
  <p>The problem is that the retrieved JSON must be post-processed, and only the users knows what to do because it heavily depends on the JSON. My idea is to have a property named postProcessData, which is the function to post process data. An incomplete example of its use is <a href="https://github.com/donpir/polywc-data-table/blob/e6b4581dd2836a3cfdfb85e09753a84fae698228/demo/index-rest.html" rel="nofollow">Here</a>. Is this the correct way to design it or I'm missing something?</p>