Making a observable variable as null

Question

I have a an observable variable of the following format:

var obvar = ko.observable("");

obvar({view:'dummy.html',model:'dummymodel'});

In one of my checks I want to empty the contents , if variable "obvar" contains

{view:'dummy.html',model:'dummymodel'}.

I tried obvar(""); but its not happening. obvar =""; would convert it to normal string. How to empty the contents?

Answer 1

Your first code snippet:

var obvar = ko.observable("");

obvar({view:'dummy.html',model:'dummymodel'});

has a special but important feature. The obvar observable first contains a string, and after the second line it contains an Object.

Your requirement that you mention is (emphasis mine):

...I want to empty the contents, if variable obvar contains {view:'dummy.html',model:'dummymodel'}

It's unclear to me what you mean by "empty" the contents, and perhaps to you as well (since you've tried obvar("");, which in a sense "empties" the content, but it had not the desired result).

At any rate, here are two ways to do it, in a runnable snippet so you can see proof that it's working:

function ViewModel() {
  var self = this;
  
  var obvar = ko.observable("");
  obvar({view:'dummy.html',model:'dummymodel'});
  
  self.obvar = obvar; // Expose it so the view can demo the workings.
  
  function canEmptyContents() { 
    // empty the contents if variable "obvar" contains {view:'dummy.html',model:'dummymodel'}
    return obvar().view === 'dummy.html' && obvar().model === 'dummymodel';
  }
  
  self.option1 = function() {
    if (canEmptyContents()) {
      obvar("");
    }
  };
  
  self.option2 = function() {
    if (canEmptyContents()) {
      obvar({ dummy: "", model: "" });
    }
  };
}

ko.applyBindings(new ViewModel());

<script src="https://cdnjs.cloudflare.com/ajax/libs/knockout/2.3.0/knockout-min.js"></script>

<button data-bind="click: option1">Option 1: empty with string</button>
<button data-bind="click: option2">Option 2: empty with empty object</button>
<hr>
Debug info: <pre data-bind="text: ko.toJSON($root, null, 2)"></pre>