javascript - Knockout Mapping overwriting Computed Observables, is this intentional? -

say, have setup below:

var model = function() {     this.base = ko.observable("initial");     this.dependent = ko.computed(function() {         return this.base() + ", computed";     }, this); };  var vm = new model(); 

at point, vm object { base: observable(), dependent: dependentobservable() } (as expected)

but, once run:

ko.mapping.fromjs({base: "hello", dependent: "hi"}, {}, vm) 

vm becomes object { base: observable(), dependent: "hi", __ko_mapping__: object }

dependent no longer observable, expecting untouched.

is intentional? if so, rationale behind this? shouldn't dependent observables kept out of mapping?

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the reason question that, using ko.mapping.tojs() convert vm javascript object (which gives dependent property, expected).

then, sometime later, i'm using ko.mapping.fromjs() shown above. combination overwrites vm's ko.computed() property.

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solutions come with:

• explicitly specify dependent ignored during mapping.

  ko.mapping.fromjs({base: "hello", dependent: "hi"}, {'ignore': "dependent"]}, vm) 

• make dependent writable (just namesake)

  this.dependent = ko.computed({     read: function() {         return this.base() + ", computed";     },     write: function() {},     owner:  }); 

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misc. info

• the line overwrites dependentobservable() (as far can understand)