Unable to parse bindings js error using ko.mapping.fromJSON with parse exist view model

Question

I want to save view model in the hidden field in JSON format. All work fine.

But when I try to get it - I get error:

Uncaught Error: Unable to

Answer 1

You are calling the ko.mapping.fromJSON with wrong arguments.

The correct usage in your case is the following:

var viewModelDeserialized = 
    ko.mapping.fromJSON(serializedJsonString, {} /* empty options */, viewModel);

Demo fiddle. (without the binding error)

The usage of the ko.mapping.fromJSON method is a little bit tricky:

• you can call it with one argument: providing just the data e.g var viewModel = ko.mapping.fromJSON(data) in this case it will return the created viewModel

• you can call with two arguments:

  • if the second argument is a ko mapping created viewModel then it is treated as the mapping target ko.mapping.fromJSON(data, koMappingCreatedViewModel)
  • otherwise the second argument is treated as the mapping options (this happens in your case) var viewModel = ko.mapping.fromJSON(data, options)

• you can call it with three arguments explicitly specifing the data, mapping and target: ko.mapping.fromJSON(data, options, target)