observableBehaviors.js

describe('Observable', function() {
    it('Should be subscribable', function () {
        var instance = new ko.observable();
        expect(ko.isSubscribable(instance)).toEqual(true);
    });

    it('Should advertise that instances are observable', function () {
        var instance = new ko.observable();
        expect(ko.isObservable(instance)).toEqual(true);
    });

    it('Should be able to write values to it', function () {
        var instance = new ko.observable();
        instance(123);
    });

    it('Should be able to write to multiple observable properties on a model object using chaining syntax', function() {
        var model = {
            prop1: new ko.observable(),
            prop2: new ko.observable()
        };
        model.prop1('A').prop2('B');

        expect(model.prop1()).toEqual('A');
        expect(model.prop2()).toEqual('B');
    });

    it('Should advertise that instances can have values written to them', function () {
        var instance = new ko.observable(function () { });
        expect(ko.isWriteableObservable(instance)).toEqual(true);
    });

    it('Should be able to read back most recent value', function () {
        var instance = new ko.observable();
        instance(123);
        instance(234);
        expect(instance()).toEqual(234);
    });

    it('Should initially have undefined value', function () {
        var instance = new ko.observable();
        expect(instance()).toEqual(undefined);
    });

    it('Should be able to set initial value as constructor param', function () {
        var instance = new ko.observable('Hi!');
        expect(instance()).toEqual('Hi!');
    });

    it('Should notify subscribers about each new value', function () {
        var instance = new ko.observable();
        var notifiedValues = [];
        instance.subscribe(function (value) {
            notifiedValues.push(value);
        });

        instance('A');
        instance('B');

        expect(notifiedValues.length).toEqual(2);
        expect(notifiedValues[0]).toEqual('A');
        expect(notifiedValues[1]).toEqual('B');
    });

    it('Should be able to tell it that its value has mutated, at which point it notifies subscribers', function () {
        var instance = new ko.observable();
        var notifiedValues = [];
        instance.subscribe(function (value) {
            notifiedValues.push(value.childProperty);
        });

        var someUnderlyingObject = { childProperty : "A" };
        instance(someUnderlyingObject);
        expect(notifiedValues.length).toEqual(1);
        expect(notifiedValues[0]).toEqual("A");

        someUnderlyingObject.childProperty = "B";
        instance.valueHasMutated();
        expect(notifiedValues.length).toEqual(2);
        expect(notifiedValues[1]).toEqual("B");
    });

    it('Should notify "beforeChange" subscribers before each new value', function () {
        var instance = new ko.observable();
        var notifiedValues = [];
        instance.subscribe(function (value) {
            notifiedValues.push(value);
        }, null, "beforeChange");

        instance('A');
        instance('B');

        expect(notifiedValues.length).toEqual(2);
        expect(notifiedValues[0]).toEqual(undefined);
        expect(notifiedValues[1]).toEqual('A');
    });

    it('Should be able to tell it that its value will mutate, at which point it notifies "beforeChange" subscribers', function () {
        var instance = new ko.observable();
        var notifiedValues = [];
        instance.subscribe(function (value) {
            notifiedValues.push(value ? value.childProperty : value);
        }, null, "beforeChange");

        var someUnderlyingObject = { childProperty : "A" };
        instance(someUnderlyingObject);
        expect(notifiedValues.length).toEqual(1);
        expect(notifiedValues[0]).toEqual(undefined);

        instance.valueWillMutate();
        expect(notifiedValues.length).toEqual(2);
        expect(notifiedValues[1]).toEqual("A");

        someUnderlyingObject.childProperty = "B";
        instance.valueHasMutated();
        expect(notifiedValues.length).toEqual(2);
        expect(notifiedValues[1]).toEqual("A");
    });

    it('Should ignore writes when the new value is primitive and strictly equals the old value', function() {
        var instance = new ko.observable();
        var notifiedValues = [];
        instance.subscribe(notifiedValues.push, notifiedValues);

        for (var i = 0; i < 3; i++) {
            instance("A");
            expect(instance()).toEqual("A");
            expect(notifiedValues).toEqual(["A"]);
        }

        instance("B");
        expect(instance()).toEqual("B");
        expect(notifiedValues).toEqual(["A", "B"]);
    });

    it('Should ignore writes when both the old and new values are strictly null', function() {
        var instance = new ko.observable(null);
        var notifiedValues = [];
        instance.subscribe(notifiedValues.push, notifiedValues);
        instance(null);
        expect(notifiedValues).toEqual([]);
    });

    it('Should ignore writes when both the old and new values are strictly undefined', function() {
        var instance = new ko.observable(undefined);
        var notifiedValues = [];
        instance.subscribe(notifiedValues.push, notifiedValues);
        instance(undefined);
        expect(notifiedValues).toEqual([]);
    });

    it('Should notify subscribers of a change when an object value is written, even if it is identical to the old value', function() {
        // Because we can't tell whether something further down the object graph has changed, we regard
        // all objects as new values. To override this, set an "equalityComparer" callback
        var constantObject = {};
        var instance = new ko.observable(constantObject);
        var notifiedValues = [];
        instance.subscribe(notifiedValues.push, notifiedValues);
        instance(constantObject);
        expect(notifiedValues).toEqual([constantObject]);
    });

    it('Should notify subscribers of a change even when an identical primitive is written if you\'ve set the equality comparer to null', function() {
        var instance = new ko.observable("A");
        var notifiedValues = [];
        instance.subscribe(notifiedValues.push, notifiedValues);

        // No notification by default
        instance("A");
        expect(notifiedValues).toEqual([]);

        // But there is a notification if we null out the equality comparer
        instance.equalityComparer = null;
        instance("A");
        expect(notifiedValues).toEqual(["A"]);
    });

    it('Should ignore writes when the equalityComparer callback states that the values are equal', function() {
        var instance = new ko.observable();
        instance.equalityComparer = function(a, b) {
            return !(a && b) ? a === b : a.id == b.id
        };

        var notifiedValues = [];
        instance.subscribe(notifiedValues.push, notifiedValues);

        instance({ id: 1 });
        expect(notifiedValues.length).toEqual(1);

        // Same key - no change
        instance({ id: 1, ignoredProp: 'abc' });
        expect(notifiedValues.length).toEqual(1);

        // Different key - change
        instance({ id: 2, ignoredProp: 'abc' });
        expect(notifiedValues.length).toEqual(2);

        // Null vs not-null - change
        instance(null);
        expect(notifiedValues.length).toEqual(3);

        // Null vs null - no change
        instance(null);
        expect(notifiedValues.length).toEqual(3);

        // Null vs undefined - change
        instance(undefined);
        expect(notifiedValues.length).toEqual(4);

        // undefined vs object - change
        instance({ id: 1 });
        expect(notifiedValues.length).toEqual(5);
    });

    it('Should expose an "update" extender that can configure the observable to notify on all writes, even if the value is unchanged', function() {
        var instance = new ko.observable();
        var notifiedValues = [];
        instance.subscribe(notifiedValues.push, notifiedValues);

        instance(123);
        expect(notifiedValues.length).toEqual(1);

        // Typically, unchanged values don't trigger a notification
        instance(123);
        expect(notifiedValues.length).toEqual(1);

        // ... but you can enable notifications regardless of change
        instance.extend({ notify: 'always' });
        instance(123);
        expect(notifiedValues.length).toEqual(2);

        // ... or later disable that
        instance.extend({ notify: null });
        instance(123);
        expect(notifiedValues.length).toEqual(2);
    });

    it('Should be possible to replace notifySubscribers with a custom handler', function() {
        var instance = new ko.observable(123);
        var interceptedNotifications = [];
        instance.subscribe(function() { throw new Error("Should not notify subscribers by default once notifySubscribers is overridden") });
        instance.notifySubscribers = function(newValue, eventName) {
            interceptedNotifications.push({ eventName: eventName || "None", value: newValue });
        };
        instance(456);

        expect(interceptedNotifications.length).toEqual(2);
        expect(interceptedNotifications[0].eventName).toEqual("beforeChange");
        expect(interceptedNotifications[1].eventName).toEqual("None");
        expect(interceptedNotifications[0].value).toEqual(123);
        expect(interceptedNotifications[1].value).toEqual(456);
    });
});