knockout's viewModel does not get updated - json

Question

I have the following knockout's viewModel :
var viewModel={
businessName: "",
....
}
I also tried to identify the field like this: businessName: ko.observable("")
Then, I have a load method that requests for a JSon with a newly populated data
And this is how I'm trying to apply the new data:
$.ajax({
//
url: "#Html.Raw(#Url.Action("Load"))",
type: "post",
data: ko.toJSON(this),
contentType: "application/json",
success: function (result) {
//OPTION 1:
viewModel.businessName = result.vm.BusinessName;
//OPTION 2:
var viewModel2 = ko.mapping.fromJS(result.vm);
console.log(viewModel2.businessName);
}
});//ajax
As a result:
if I use Option1, I get the new data but it does not get updated on the page.
If I use Option2, it writes "undefined"
Please advise how can I update the new data on the page?
I checked the similar topics but there is no answer that helps
PS
It seems I resolved OPTION 1. But still don't understand why OPTION 2 does not work

Answer 1

ko.observable is a function, not a property. So you get it's value like this:
var whatsTheValue = myVM.MyObservable();
and you set it like this:
myVM.MyObservable(newValue);
This is all in the docs.
Note, however, when using the data-bind syntax in your HTML, you don't need to explicitly unwrap your observable by using the parenthesis because KO is smart enough to do it automatically:
<span data-bind="text: MyObservable"></span>

Answer 2

You have to use ko.observable in the ViewModel and access/write it accordingly.
var myViewModel = {
businessName = ko.observable('')
};
...
$.ajax({
...
success: function(result) {
myViewModel.businessName(result.vm.BusinessName);
},
...
});
Otherwise your view won't have any clue you changed businessName. In the implementation ko.observable, besides actually storing the new value, broadcasts some events to your view, letting it know the stored value changed.