A Dart Polymer behavior that provides a Polymer element with a model derived from an ajax request.
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Pub Travis

A Dart Polymer behavior that provides a Polymer element with a model derived from an ajax request.


First, make your model class implement AjaxBackedModel and its abstract method setFromJsonString. This method handles deserialization of JSON into an existing instance of the model.

Next, create a Polymer element that will utilize the model, by implementing AjaxBackedModelBehavior. The element must implement get modelInstance which returns an instance of the model class above.

With the above wiring, the polymer element gains additional attributes which simplify its use. For example:

<my-element auto-load ajax-url="http://mydomain/api/data.json"></my-element>

With the usage above, the json returned from data.json will be converted to the model object and assigned to the "ajaxModel" attribute when the element is readied. The element's html can reference model data as [[ajaxModel.myField]].


  • ajax-url: The url to the data source, e.g. a rest endpoint or data file
  • auto-load: if true, then any changes to ajax-url will result in the model being updated with the result of a new ajax request.
  • ajax-model: may be used to set the model directly for situations where it is not necessary to look up the model via ajax


AjaxBackedModelBehavior may fire the following three events

  • ajax-model-request, detail: String containing url
  • ajax-model-response, detail: AjaxBackedModel
  • ajax-model-error, detail: Map containing 'status' and 'statusText'

Changing the model attribute name

If desired, the model attribute name can be changed from the default ("ajaxModel"). Override the method get modelName. See example.

Future improvements

I would like to provide a @AjaxModel annotation, and create a transformer automatically provide the wiring described above.


The following code illustrates a simple example of a model and a custom Polymer element using it an ajax backed model.

class Country extends Object with AjaxBackedModel, JsProxy {

  @reflectable int id;
  @reflectable String name;


  setFromJsonString(String json) {
    id = o['id'];
    name = o['country'];

class CountryDetail extends PolymerElement with AjaxBackedModelBehavior {

  CountryDetail.created() : super.created();

  AjaxBackedModel get modelInstance => new Country();


An full example can be found in the example directory and run via pub serve example or viewed online


To run on dartium (default): pub run test As usual, tests can be run on other platforms with -p<platform>

To run tests as javascript, the pub serve and test execution must be performed separately. Run pub serve test --port=8080 from one terminal and pub run test -pchrome --pub-serve=8080 from a second.

Note that tests are specifically blocked from running on Firefox currently in order to utilize Travis CI.