Subscribers to knockout observables are notified as soon as the observable changes

knockout-subscribables.js

// src/subscribables/subscribable.js

    "notifySubscribers": function (valueToNotify, event) {
        event = event || defaultEvent;
        if (this._subscriptions[event]) {
            ko.dependencyDetection.ignore(function() {
                ko.utils.arrayForEach(this._subscriptions[event].slice(0), function (subscription) {
                    // In case a subscription was disposed during the arrayForEach cycle, check
                    // for isDisposed on each subscription before invoking its callback
                    if (subscription && (subscription.isDisposed !== true))
                        subscription.callback(valueToNotify);
                });
            }, this);
        }
    },
    
// src/subscribables/observable.js
ko.observable = function (initialValue) {
    var _latestValue = initialValue;

    function observable() {
        if (arguments.length > 0) {
            // Write

            // Ignore writes if the value hasn't changed
            if ((!observable['equalityComparer']) || !observable['equalityComparer'](_latestValue, arguments[0])) {
                observable.valueWillMutate();
                _latestValue = arguments[0];
                if (DEBUG) observable._latestValue = _latestValue;
                observable.valueHasMutated();
            }
            return this; // Permits chained assignments
        }
        else {
            // Read
            ko.dependencyDetection.registerDependency(observable); // The caller only needs to be notified of changes if they did a "read" operation
            return _latestValue;
        }
    }
    ...
    observable.valueHasMutated = function () { observable["notifySubscribers"](_latestValue); }
    observable.valueWillMutate = function () { observable["notifySubscribers"](_latestValue, "beforeChange"); }
    ...

    return observable;
}