Take a look at the working CodePen here: http://codepen.io/djskinner/pen/JdpwyY
// Animation start events push here
var startBus = new Bacon.Bus();
// Animation end events push here
var endBus = new Bacon.Bus();
// Balance updates push here
var balanceBus = new Bacon.Bus();
// A Property that determines if animating or not
var isAnimating = Bacon.update(false,
[startBus], function() { return true; },
[endBus], function() { return false; }
);
// Only update the displayBalance when not animating
var displayBalance = Bacon.update(0,
[balanceBus.holdWhen(isAnimating)], function(previous, x) {
return x;
}
);
setTimeout(function() {
var streamTemplate = Bacon.combineTemplate({
balance: displayBalance
});
// Uncommenting this block changes the way the system behaves
// streamTemplate.onValue(function(initialState) {
// console.log(initialState);
//})();
// Print the displayBalance
streamTemplate.onValue(function(v) {
console.log(v.balance);
});
});
Pressing the balance button generates a new random number. A Property is created that uses holdWhen to restrict balance updates coming through until the isAnimating Property becomes false.
If I was interested in getting the initial state of streamTemplate, I might get the value and immediately unsubscribe:
streamTemplate.onValue(function(initialState) {
console.log(initialState);
})();
However, once I do this the displayBalance Property behaves differently and I no longer receive updates.
Why would this seemingly inert change make such a drastic different to the system? Surely the behaviour of the system shouldn't be dependent on whether someone has subscribe and unsubscribed to the streamTemplate at some point in the past?
