Question

I’m trying to write a jasmine spec for a computed observable like below:

self.positionDate = ko.computed(function () {
  var dateString = "";
  var start = moment(self.positionStartDate()).format("LL");
  var end = moment(self.positionEndDate()).format("LL");
  if (start !== end) {
    dateString = sprintf("%s - %s", start, end);
  }
  else {
    dateString = sprintf("%s", start);
  }
  return dateString;
}).extend({ throttle: 1 });

With the throttle, the positionDate computed function is not getting updated. I’ve tried artificially waiting as well as calling valueHasMutated() both to no avail.

Has anyone successfully written a spec on a throttled computed?

Answer 1

Because of the usage of the throttle you made your observable “async” so you need to use the asynchronous specs features in Jasmine.

So you need to use the runs and waits functions something like:

describe('throttled obserable', function () {

    it('positionDate should be changed after positionStartDate changed', 
      function () {
        var vm = new ViewModel();

        runs(function () {
            vm.positionStartDate('January 21 2013');
            vm.positionEndDate('January 22 2013');
        });

        waits(1);

        runs(function () {
            expect(vm.positionDate())
                 .toEqual('January 21 2013 - January 22 2013');
            vm.positionStartDate('January 20 2013');
        });

        waits(1);

        runs(function () {
            expect(vm.positionDate())
                 .toEqual('January 20 2013 - January 22 2013');
        });
    });
});

Demo JSFiddle.