Is there any kind of wildcard operator in the Durandal observable plugin, to subscribe to a change in any property?

Question

Is there any kind of wildcard operator in the Durandal observable plugin, as there is in (for example) JsObservable?

The Durandal observable documentation gives this example:

var observable = require('plugins/observable');

var viewModel:{
    firstName:'',
    lastName:''
};

observable(viewModel, 'firstName').subscribe(function(value){
    console.log('First name changed.');
});

viewModel.firstName = 'Test';

What I'd like to do is use a wildcard to subscribe to any changed property on the target. Something like this:

observable(viewModel, '*').subscribe(function(property, value){
        console.log(property + ' changed.');
    });

I don't see anything in the API documentation, but wondered if there was anything undocumented, or if anyone has a workaround to implement this behaviour.

score 1 · Answer 1 · answered Apr 25 '14 at 09:45

1

Unfortunately, there is no wildcard operator for this functionality.

But you can easily create wrapper module for this functionality.

Here is small example:

var observable = require('plugins/observable');

var wildcardObservable = function(obj, changeCallback){
  for(var prop in obj){
    observable(obj, prop).subscribe(changeCallback);
  }
}

var changeCallback = function() {
  console.log('property changed.');
  }

Usage:

  var viewModel:{
    firstName:'',
    lastName:''
  };

wildcardObservable(viewModel, changeCallback);

answered Apr 25 '14 at 09:45

Dmitry Zaets

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But - it doesn't say which property has been modified, which makes its utility very limited. – Jude Fisher Apr 30 '14 at 18:40
You can also use this.target inside callback to get observable itself. But as far as I seen in sources of KnockoutJs there is no possibility to get name of Observable variable inside of subscribe function, only new value (it is passed as argument). – Dmitry Zaets May 05 '14 at 06:44

score 0 · Answer 2 · answered May 07 '14 at 00:22

With thanks to U10 for the start above, (and with reference to a few examples on the web) I came up with the following, which uses a closure to track all the necessary properties. It's a bit messy but it does what I need for now - hopefully it will be of use to someone.

var ChangeTracker = (function () {
        function ChangeTracker() {
        }
        ChangeTracker.prototype._trackChange = function (prop, target) {
            var type = typeof (target[prop]);
            var value = target[prop];
            _logger.log("_trackChange", { target: target, prop: prop, type: type, value: value }, "CT");
            _obs(target, prop).subscribe(function (newValue) {
                var obj = {
                    target: target,
                    prop: prop,
                    newValue: newValue,
                    oldValue: value
                };
                _logger.log(">>>>>>>>>>>>>>> CHANGE!", obj, "CT");
                value = newValue;
            });
        };

        ChangeTracker.prototype.TrackChanges = function (target) {
            var _this = this;
            for (var prop in target) {
                if (target.hasOwnProperty(prop)) {
                    this._trackChange(prop, target);
                }
                var underlying = ko.utils.unwrapObservable(target[prop]);
                if (underlying instanceof Array) {
                    ko.utils.arrayForEach(underlying, function (item) {
                        _this.TrackChanges(item);
                    });
                } else if (typeof underlying === "object") {
                    this.TrackChanges(underlying);
                }                
            }
            }
        };
        return ChangeTracker;
    })();

Is there any kind of wildcard operator in the Durandal observable plugin, to subscribe to a change in any property?

2 Answers2