Globe observer

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Explorers have been navigating the globe for centuries. Circumnavigation refers to traveling around something like the continent or any astrological body. The circumnavigation distance should encompass going around the object around the great circle.The great circle distance on earth is about 40,000km which is the minimum distance required to circumnavigate the globe. The most efficient way of circumnavigating the earth is by passing through at least one pair of antipodal points and covering the minimum distance of the equator and spending equal time in both the northern and southern hemispheres. 15. Magellan-Elcano Expedition Magellan Elcano expedition was a Spanish voyage and the first to circumnavigate the world under the command of Ferdinand Magellan, a Portuguese explorer in search of a maritime route to Spice Island, Indonesia. Although Ferdinand was killed en route in the present day the Philippines, his crew comprising of 18 members completed the round the world voyage under the command of Sebastián Elcano on September 6, 1522. 14. Francis Drake Francis Drake, a renowned pirate of slaving voyages in the 16th century, was sent to South America in 1577 by Queen Elizabeth II to intercept the gold, silver, and jewelry that the Spanish were shipping to Spain across the Isthmus of Panama.Drake was successful in capturing twenty-six tons of silver, half a ton of gold, and pieces of jewelry. Since he could not sail back along South America, he proceeded to north California traversing through North and South America, Asia, Africa and returning to Europe in 1580 becoming the second person to circumnavigate the globe. 13. Martín Ignacio de Loyola Martín Ignacio was a renowned missionary in India and China, who circumnavigated the globe twice in his lifetime. His first circumnavigation was made in a westerly direction from 1582-1584 from the Canary Islands while the second was made in an easterly direction between 1585 and 1589. On both accounts, Ignacio took advantage of the crown of Phillip II of Spain which united Spain and Portugal. 12. Pedro Cubero Pedro was an ordained Spanish priest who enjoyed traveling the world in pursuit of his missionary work. In 1670. Pedro embarked on a journey to East Asia that eventually led him to circumnavigate the globe through the eastern direction. Unlike his predecessors who circumnavigated the globe through marine voyages, Pedro embarked on a land voyage through Western and Eastern Europe, Western and Central Asia and North America. 11. Giovanni Francesco Gemelli Careri Francesco Careri was a famous 17th-century Italian adventurer and traveler. He undertook an around-the-world trip through land and water in five years by securing passage in trade ships. His trip, which was mainly done for pleasure rather than profit, was recorded in the sixth volume of the Giro Del Mondo, which gives detailed accounts of all the countries he visited. 10. William Dampier William Dampier was a great English explorer who explored modern day Australia and became the first person to circumnavigate the world three times. As a buccaneer, sea captain, author and scientific observer, William traveled

That implements the Subject interface: // Subjectclass Store implements Subject {} Next, initialize the Subject’s state in the Store class. The subject’s observers will react to changes to this state. In this case, the state is a number, and the observers will react to an increase in the number: // Subject stateprivate numberOfProducts: number; Next, initialize an array of observers. This array is how you'll keep track of the observers: // initializing observersprivate observers: Observer[] = []; You might find some implementations of the observer pattern using a Set data structure in place of an array to keep track of the observer. Using a Set will ensure that the same observer won’t appear twice. If you want to use an array instead, you should check for duplicate observers in your attach method. Next, you should implement the Subject’s methods—attach, detach, and notify/update—in your concrete class. To implement the attach method, first check if the observer is already attached and throw an error if it is. Otherwise, add the observer to the array using the JavaScript array method, push: // Attaching Observer(s)attachObserver(observer: Observer): void { // Check if the observer has already been attached const observerExists = this.observers.includes(observer); if (observerExists) { throw new Error('Observer has already been subscribed '); } // Add a new observer this.observers.push(observer);} Next, implement your detach method by finding the index and removing it from the array using the JavaScript splice method. There can be scenarios where the observer you are trying to detach has already been detached or was not subscribed in the first place. You should handle these scenarios by adding a conditional statement to check if the observer is in the array or the set as the case may be. // Detaching Observer(s)detachObserver(observer: Observer): void { console.log(`Detaching observer ${JSON.stringify(observer)}`); const observerIndex = this.observers.indexOf(observer); if

A design pattern is a template that solves a commonly recurring problem in software design. The observer pattern, also known as the publish-subscribe pattern, is a behavioral pattern. It allows you to notify multiple objects or subscribers about any event that is published in the object they’re observing. Here you will learn how to implement the observer design pattern in TypeScript. The Observer Pattern The observer pattern works by defining a one-to-many relationship between the publisher and its subscribers. When an event occurs in the publisher, it will notify all subscribers to that event. One widespread example of this pattern is JavaScript event listeners. For context, assume you’re building an inventory tracker that keeps track of the number of products in your store. In this case, your store is the subject/publisher, and your inventory is the observer/subscriber. Using the observer design pattern would be optimal in this situation. In the observer design pattern, your subject class must implement three methods: An attach method. This method adds an observer to the subject. A detach method. This method removes an observer from a subject. A notify/update method. This method notifies the subject’s observers when the state changes in the subject. Your observer class must implement one method, the update method. This method reacts when there’s a change in its subject’s state. Implementing the Subject and Observer Classes The first step to implementing this pattern is to create interfaces for the subject and observer class, to ensure that they implement the correct methods: // Subject/Publisher Interfaceinterface Subject { attachObserver(observer: Observer): void; detachObserver(observer: Observer): void; notifyObserver(): void;} // Observer/Subscriber Interfaceinterface Observer { update(subject: Subject): void;} The interfaces in the code block above define the methods your concrete classes must implement. A Concrete Subject Class The next step is to implement a concrete subject class