Question

I’m new to Knockout and even though I’ve used an observable pattern library before, I don’t know how to set a function to observe a value in the ViewModel and to trigger when that value changes.

The situation is like this:
I’d like a modal popup to be enabled when the value of a dropdown is “other”. I’m using the Twitter bootstrap “dropdown” (which is really a list of anchors) and each anchor has a click binding to a function on the ViewModel called setDetail. setDetail sets the value of an observable property called problem.

My thinking is to put a function to observe the value of problem in order to keep the logic separate. Is there a way to do this or should I put the code in the setDetail function?

Any help is appreciated!

Answer 1

Yes, you can explicitly subscribe to an observable.

The documentation is available here, search for Explicitly subscribing to observables.

You would be doing something like:

function ViewModel() {
  this.problem = ko.observable();
  this.problem.subscribe(function(newValue) {
    if (newValue === 'other') {
      // trigger modal
    }
  });
}