`$watchAsProperty` may emit duplicate value changes upon start

[timmolendijk]

Consider the following lines of code:

$scope.test = 'initial';

var property = $scope.$watchAsProperty('test');

// Property will emit the scope variable's initial value
property.onValue(function (value) {
    console.log("I will be invoked twice with the same value:", value);
});

// Running the digest loop will run the Angular watch that feeds `property` and the same value will be emitted once more.
$scope.$digest();

It will log twice with value 'initial'. I understand why that technically happens, but I consider it very much counter-intuitive.

In my opinion, how one expects $watchAsProperty to behave is very obvious and intuitive: it should represent an Angular scope variable as Bacon property. In the context of this issue that means that it should only emit a value change once for the scope variable that is assigned to 'initial' at the very beginning and is left untouched from that point on.

I suggest changing the implementation of $watchAsProperty to check for equality in its Angular watch function, as also referred to in the Angular documentation (see last paragraph of $watch section and second example).

More specifically I suggest replacing the current watch function with:

scope[watchMethod](watchExp, function(newValue, oldValue) {
    if (newValue !== oldValue) {
        return bus.push(newValue);
    }
}, objectEquality);

This would prevent the confusingly duplicate value change events.