Knockout JS: mapping.fromJS stripping out observable attributes of object when added

Question

I have the following ko.mapping and an object (coffeescript):

form_fields = ko.mapping.fromJS []

obj =
  name: ko.observable 'some_name'
  type: ko.observable 'some_type'
  avail_values: ko.observableArray some_array
  vals: ko.observableArray some_other_array_of_observables

I've verified that obj is being populated as expected by knockout observable functions. If I call obj.name() I get the expected value back, for example.

However, when I do form_fields.push obj OR ko.mapping.fromJS [obj], form_fields , form_fields is populated with an empty object. The object exists within the array, but it has no attributes at all.

Here's the resulting array in the chrome dev tools:

Do I need to do something else to accomplish this?

Answer 1

Use

ko.mapping.fromJS [obj], {}, form_fields

The empty object in the middle is the mapping rules , a parameter which is required when you specify a mapping target.