Pager JS parameters and Knockout

Question

I'm using Pager JS, Knockout and Jquery in my web application. Here's the code

function ViewModel(){
  var self = this;

  self.interior = ko.observable();
  self.interior.background = ko.computed(function() {
    $.getJSON('/interiors', {interior_id:  self.interior_id()}).success(function(data) {
      return self.interior.background = data.interior.background_url;
    });
  }, this);

}

$(document).ready(function () {

  pager.Href.hash = "#!/";
  viewModel = new ViewModel();
  pager.extendWithPage(viewModel);
  ko.applyBindings(viewModel);
  pager.start();

});

When the code is executed I get the following error:

Uncaught TypeError: Object #<ViewModel> has no method 'interior_id' 

I understand that the variable does not exist yet, and she do not have a method. But how to get around this error?

Answer 1

If the interior_id gets added to your viewmodel later then you can use the deferEvaluation option on your ko.computed so it only evaluates its function when the background property gets accessed and not when your ViewModel is created:

self.interior.background = ko.computed(function() {
    //do stuff
}, this, {deferEvaluation: true});