Question

I would like to bind a visible property to be true when one of two conditions are true. Something like the following

 <tr data-bind="visible: active || $parent.displayDeactive">....</tr>

My code works when I do one or the other bindings but not when I put the || in there. I haven’t found any documentation that says I can put any logic in this binding, but if I can’t do it directly what is the est way to do it since I am binding a property of a template and one object of the $parent viewmodel.

Answer 1

If you are using the value of an observable in an expression then you need to reference them as a function. So, if active and displayDeactive are observables you would do:

data-bind="visible: active() || $parent.displayDeactive()"

There are a few ways to move it to the view model, you could:

• create a computed observable on the child (function would need to be able to reference the parent)
• create a function on the parent that takes in the child and returns your value (bindings are executed in a computed observable, so it will fire again when any observable that it accesses changes)
• create a function on the child that takes in the parent and returns the value (same note as above)

Sample of logic in the binding and using a function on the parent here: http://jsfiddle.net/rniemeyer/f6ZgH/