Knockout.js Value Binding Triggered By Unusual Keys In Version 2.2.0

Consider the following trivial example: In knockoutjs 2.1.0, when I press any of ctrl,Up arrow,Down arrow,Shif

Solution 1:

I followed the subscribe method suggested above, but it seemed a little messy and not in the spirit of knockout. A colleague suggested writing an extender that would suppress the binding in the case of no change (which would emulate the 2.1 behaviour):

ko.extenders.suppressNoChange= function(target) {
    var result = ko.computed({
        read: target,
        write: function(newValue) {
            var current = target();
            if (newValue!== current) {
                target(newValue);
            }
        }
    });
    result(target());
    return result;
};

so now we can extend our computed observables such that the binding will not fire in the case where no change has occurred.

We can use it as follows:

ko
  .computed({
     read: function(){},
     write: function(v){})
  .extend({
     suppressNoChange: null
  });

and allows me to make very minimal changes to the 2.2 fiddle in the question to restore the 2.1 behaviour.

See http://jsfiddle.net/Rmcza/26/

Solution 2:

I think this is a result of this change made by RP Niemeyer in Sept. It causes computed observables to always write when triggered, even if the value hasn't changed.

You will notice in this fiddle that this does not occur when using a non-computed observable. I tested this using an explicit subscription, and the event does not fire for the down arrow.

this.test = ko.observable('');
this.test.subscribe(function(newValue) {
    alert("The test value new name is " + newValue);
});

Maybe Ryan can explain why this was changed, and why computed's are behaving differently than regular observables in this case. You might want to make an issue on the GitHub page.