Observer pattern - simple implementation

Observer.js

/**
 * Observer pattern - simple implementation
 * By Michał Miszczyszyn, 2016
 */

class Observer {
    constructor() {
        this.observers = [];
    }

    addObserver(observer) {
        this.observers.push(observer);
    }

    removeObserver(observer) {
        const index = this.observers.indexOf(observer);
        if (index === -1) {
            return;
        }

        this.observers.splice(index, 1);
    }

    notify(data) {
        this.observers.forEach(observer => {
            observer(data);
        });
    }
}

Observer.spec.js

describe('Observer', () => {
    it('should observe changes', () => {
        const observer = new Observer();
        const callback1 = jasmine.createSpy('callback1');
        const callback2 = jasmine.createSpy('callback2');

        observer.addObserver(callback1);
        observer.addObserver(callback2);
        observer.notify('test1');

        expect(callback1).toHaveBeenCalledWith('test1');
        expect(callback2).toHaveBeenCalledWith('test1');
    });

    it('should remove observer', () => {
        const observer = new Observer();
        const callback1 = jasmine.createSpy('callback1');
        const callback2 = jasmine.createSpy('callback2');
        const callback3 = jasmine.createSpy('callback3');

        observer.addObserver(callback1);
        observer.addObserver(callback2);
        observer.addObserver(callback3);
        observer.removeObserver(callback2);
        observer.notify('test1');

        expect(callback1).toHaveBeenCalledWith('test1');
        expect(callback3).toHaveBeenCalledWith('test1');
        expect(callback2).not.toHaveBeenCalled();
    });
});