KnockoutJS - Assign Observable value to JavaScript variable

Question

I am trying to see if I can assign a JavaScript variable to the value of a value of a KO Observable.

The reason for this is I want to assign it to a jquery module, as a property.

I know I can do:

 var viewModel = { firstName : ko.observable("Bert"), lastName : ko.observable("Smith"), pets : ko.observableArray(["Cat", "Dog", "Fish"]), type : "Customer" }; viewModel.hasALotOfPets = ko.computed(function() { return this.pets().length > 2 }, viewModel) var jsonData = ko.toJSON(viewModel);

But, what if I don't want everything that is in the view model? Can i just only select n number of items?

Which items do you want to omit? Are there sufficiently few that you could exclude them manually? — Steve Greatrex
– Steve Greatrex, Commented May 31, 2013 at 20:09
Not necessarily. This was just an example that I provide. But for example, I would want to only get like firstName and type. I just want to know if I can only get select values. — Jesse
– Jesse, Commented May 31, 2013 at 20:22
You may be able to do something with the knockout mapping plugin, but I'm not sure of the syntax off the top of my head — Steve Greatrex
– Steve Greatrex, Commented Jun 1, 2013 at 13:44

Tom Blodget · Accepted Answer · 2013-05-31 22:21:06Z

There two concepts here:

Retrieving the object from a Knockout observable
Manipulating a JavaScript array

Code:

var start = 1; // index of Dog var n = 1; // just one item var jsonData = ko.toJSON(viewModel.pets().slice(start, start + n));

In Knockout, observables are functions. To set its value you call it with a parameter. To get its value, you call it.

JavaScript arrays have a slice function that can be used to get a smaller array.

UPDATE based on comments on the question:

If you want to take n fields from viewModel, ko.toJSON will work on a subsetted view model:

var n = 2; var count = 0; var subModel = {}; for (var k in viewModel) { if (count >= n) break; if (viewModel.hasOwnProperty(k)) { subModel[k] = viewModel[k]; count++; } } var jsonData = ko.toJSON(subModel);

If you want specific fields only, create a subsetted model with those:

var jsonData = ko.toJSON({ firstName: viewModel.firstName, type: viewModel.type });

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