Senior full-stack developer interview questions and answers

Pair programming is when two developers have to work together on the same terminal. It is one of the essential elements of extreme programming. In this type of programming, one developer types the codes and is called the “driver”, while the other programmer reviews the codes and is called the “navigator”.

CORS stands for Cross-Origin Resource Sharing. It is a process in which several web resources can be accessed on different domains. A developer can use CORS to openly integrate web scripts with the external content of the original domain. This can help with improved integration between web services.

Continuous integration is a process in which codes specially designed and automated for testing are used. With this process, developers can deploy codes when production is going on. In fact, web developers use continuous integration several times a day for integrating codes. In this process, the checking of codes happens automatically, therefore, leading to quick and efficient error detection.

A thread is defined as the single, sequential flow of the control within a program. It is not the program itself and cannot run on its own. In a running program, a thread may have to dig some of its own resources. For example, the execution stack and program counter must belong to that thread. The code in a given thread is useful only for that particular context. A single thread has a single point of execution i.e. only one user can manage one request at a time.

Multi-threading is a process that is used for improving CPU performance. Through this process, multiple users can manage the program at the same time or the same user can manage several requests simultaneously. Multi-threading is achieved by executing several processes that the operating system supports. For example, a web browser has multi-threads running at the same time - while you scroll through a page, you can simultaneously download an application or a document, listen to music, take a print in the background, and more. .

Scalability refers to the ability of the website to work efficiently as the workload increases and more resources, usually, hardware and software, are added. In the current era of digitalization, the data and network demands on the system are ever-increasing. Thus, it is important to improve the scalability and performance of a website to ensure the long-term success of one’s business.

For improving the scalability and efficiency of a website, you can do the following:

• Minimizing DNS lookup
• Using browser cache efficiently
• Getting rid of unnecessary images
• Minimizing redirects of URLs
• Using async or defer to avoid the parsing of Javascript
• Avoiding duplication of codes
• Using CDN to place all assets in cookie-free domains
• Not using inline JavaScript and CSS

If a program has two expressions with the same value such that they can be used in place of each other anywhere in the program without any impact on the outcome, the program is is said to have referential transparency. Referential transparency is used a lot in functional programming. So, if there is a given function and input value, the output you get will always be the same. This means that no external state is used in the function.

REST stands for Representational State Transfer. It is a style of architecture used for creating websites and web applications. It utilizes HTTP requests for accessing and using data. With its help, we can read, create, change, and delete data.

An API or Application Program Interface refers to the website code that permits the communication between two software programs. We can use it to write code for requesting services from another application or from an operating system.

When an asynchronous function returns a synchronous object, this object is called a promise. There are three states of a promise:

• Fulfilled: When the promise calls the onFulfilled() method, it is in the fulfilled state.
• Rejected: When the promise calls the onRejected() method, it is in the rejected state.
• Pending: When a promise is neither rejected nor fulfilled, it is in the pending state.

A promise is settled only when it is not pending anymore.

Long polling is a method used for getting a stable server connection without using protocols such as WebSocket or Server-Side Events. In the conventional client-server model, this method is at the top. In Node.js, the same technique is called the next development model.

The functioning of this method includes the sending of requests from the client to the server, with the server responding till the connection with new and unique information opens. When the server responds, the client can submit a request to the server. The server returns a query when there is data available. The function takes place when the application of the client and the requests of the server end.

When closing the JDBC connection, in Java, slips the developer’s mind, the situation is called a connection leak. One of the commonest connection leaks is experienced when a developer uses a connection pool like DBCP. The developer can get rid of the leak by closing the connection and managing the error-handling code.