Facebook Software Engineer Interview Questions & Answers
Behavioral
1. Facebook is very proud of our products and the people who develop them. In your opinion, what distinguishes a great software engineer from an average one?
How to Answer
When an interviewer asks this type of question, they seek to understand what your perception of excellence in this role is. When answering the question, you should align your response with the job requirements, as defined in the job posting. You can also incorporate your past performance to demonstrate that you are aware of what excellence is and strive to achieve it.
Answer Example
"I believe the trait which distinguishes a great software engineer from an average one is being able to balance excellence and performance. While I strive to write perfect code, I recognize that the project has a deadline and needs to be accomplished on time and under budget. If I have to compromise the quality of my code, it is done in such a way that it will not impact the final performance of the product."
Behavioral
2. Here at Facebook, we value work life balance and initiative. What personal software development projects have you worked on outside of work?
How to Answer
In addition to seeking candidates who have the skills and experience necessary to perform the job, hiring managers at Facebook want to make sure the individual will fit into their organization. This is why they are likely to ask you about activities outside of the workspace and personal interests you may have. Your ability to contribute to the corporate culture is equally as important as your ability to do the job. You should have some stories about your personal life prepared, just in case the interviewer asks about this.
Answer Example
"As odd as it sounds, I do enjoy programming and creating applications outside of work. I enjoy this because it allows me to test my skills and utilize new methods on applications I find interesting without the pressure of meeting a deadline or end-user requirements. I recently created a program that allows me to control several different Wi-Fi LTE devices in my home from my phone. The app has features similar to Amazon Alexa or Facebook, but with a customized interface and more efficient code."
Operational
3. If hired by Facebook, can you estimate what portion of your day will involve coding and other activities you will perform when not coding?
How to Answer
This operational question is seeking to understand how you go about doing your job on a day-to-day basis. Operational questions will ask you about the processes you use to accomplish the tasks required by this position. The best way to answer operational questions is directly and briefly. The Facebook interviewer will ask you a follow-up question if they need more information or want to explore the topic in more detail.
Answer Example
"During a normal day, I spend about 60% of my time writing code. The remainder of the day is spent reviewing my work, meeting with my manager, collaborating with other coders on my team, and learning new coding technologies and methodologies."
Operational
4. Many Facebook Software Engineers prefer to program in Java. Can you describe how you would implement linear search in JavaScript?
How to Answer
This question asks you to detail the process you use to perform a specific operation within a software programming language. During an interview, you should listen carefully to each question the interviewer asks. Always make sure that the interviewer completes the question before you begin to formulate your answer. This will ensure that you respond to the right question and provide the interviewer with the information they are seeking.
Answer Example
"The easiest way to implement a linear search within JavaScript is to create an algorithm that examines each element in the list and determines whether it matches the value I have defined. Once I've created the algorithm, I can repurpose it by simply redefining the value and/or the list I am using. This is just one of the Java programming techniques I will use if hired as a Software Engineer here at Facebook."
Operational
5. How would you implement Dijkstra's Shortest Path using a programming language with which you are familiar?
How to Answer
When asked about how you would implement a procedure or perform an operation, the interviewer hopes to learn more about how you go about doing the job for which you are interviewing. This is known as an operational question. When answering an operational question, you should step the interviewer through the process briefly and directly. It may help break the process down into smaller steps to help the interviewer better understand your methodology. You should be prepared for follow-up questions any time you answer an operational question.
Answer Example
"When programming in Ruby, I would implement Dijkstra's Shortest Path by creating an algorithm to identify the shortest path between two nodes which have positive-edge weights within the graph. I would first query my libraries to see if I have done this before or if another developer had already created a similar algorithm. If not, I would follow the guidelines within Ruby to accomplish this."
Operational
6. How do you go about organizing CSS files, and why do you prefer this approach?
How to Answer
This is an example of an operational question that has technical aspects to it. The interviewer is interested in learning more about how you go about doing your job related to this specific topic. No two interviewers are the same, so the questions you will be asked may vary from interview to interview. The best way to prepare for this is to research the company, review your resume, and spend some time reviewing the operations you perform and the technologies with which you work.
Answer Example
"The method I use to organize my CSS files is based on the file's style type. Categories I use include reset, layouts, list, carousel, tables, and several others. This enables me to quickly locate the specific style I'm looking to incorporate into the front end of my program."
Operational
7. Walk me through the steps to build a single page application with multiple sections using the programming framework in which you typically work.
How to Answer
You can often identify the type of question you're being asked by how the interviewer asks it. When you hear a phrase such as 'walk me through the steps...,' you know that this is an operational question. The best way to respond to this sort of question is to break down the process into individual steps and briefly describe each one. The interviewer at Facebook will likely ask you a follow-up question so they can better understand your methodology, so come prepared with a few examples.
Answer Example
"I generally work in Ruby, so the first thing I do when building a single page application is diagram it based on the functional and non-functional requirements. I then search my libraries to see if I have code that I can apply to the application. Then, I write the code that I need to create the application according to the user specs. Finally, I test, debug, and finalize the application before publishing it. I create documentation throughout the process so other programmers can follow my steps and modify the application."
Operational
8. What process do you use to test and find bugs in an application you've developed?
How to Answer
The Facebook interviewer will likely ask a series of questions regarding your process because they seek to understand the steps you generally take in scenarios such as this one. As an experienced software engineer, you should be able to easily describe the procedures you use to test and debug the application you develop. Since this is an operational question, your answer should be direct and to the point. You should anticipate follow-up questions.
Answer Example
"Since I typically use the agile or waterfall development processes, just as you do here at Facebook, I test my application at various stages during the development process. This allows me to correct errors before they have greater implications later in the process. I use a variety of tools to test and debug the software. I also ask my peers to review my work during the development stage. Once the application is completed, I send it to the quality assurance team for final testing and debugging."
Operational
9. Which do you prefer - a micro-service approach or a monolithic app?
How to Answer
When asking about a preference, the interviewer is seeking to understand how you approach your work. Your response to this question is based on two factors. The first is your experience and skill set in this job. The second is the research you have done about Facebook and your understanding of their preferences for the type of operations they perform. Your answer can either align with Facebook's processes or conflict with them. If you choose to conflict with them, you should be able to rationalize your answer based on your experience.
Answer Example
"While I'm aware that Facebook prefers monolithic applications, I use a micro-service approach. I like to do this because it allows me to create different services that can operate independently and, therefore, more robustly. While this approach results in better performance and more efficient code, it also creates multiple failure points. Extensive testing before putting the application into production can usually mitigate this."
Operational
10. How do you go about addressing errors in your code?
How to Answer
Nobody is perfect, even the highly-skilled software engineers Facebook hires. Every software engineer has errors in the code they create. Denying this will be a red flag, which will make the interviewer skeptical of your qualifications. A better approach to answering this question is to acknowledge that you make errors, and you have a process you use to identify and correct them.
Answer Example
"After I create a segment of code, I take several steps to identify any errors and debug them. These include wrapping the code, using try/catch statements, and using various debugging tools. Once the entire program has been completed, I ask either my peers or the quality control team to review the code and identify any errors that I may have missed."
Operational
11. Describe the process you use to create a program, from requirements definition to delivery.
How to Answer
When the interviewer asks you to describe a process, they are seeking to understand how you go about doing your job. When preparing for these types of questions, you should review the job description to fully understand the position's requirements and how the organization will expect you to do your job. You should also review the processes you currently use to ensure they align with this role's requirements. Your answer should describe each step of the process in a sequential manner. Make sure to keep your response simple and to the point.
Answer Example
"The process I use to create a program begins with gaining a thorough understanding of the requirements for the application. Once I understand these, I create a flow diagram for how I believe the application should work. I then create code for each operation within the application. I submit the final program to the quality control team, which reviews and debugs the program. The final step is to get sign off from the users. Throughout the process, I document my work so that it can be replicated or updated if needed."
Operational
12. Walk me through your process for designing scalable applications.
How to Answer
A Facebook interviewer will ask this type of question to understand how you go about doing your job. When asked to walk somebody through the process you use, you should divide it into several distinct steps and briefly describe each one. Be careful not to talk too much or over complicate your answer. If the interviewer needs more details, they will request them.
Answer Example
"The process I use for designing scalable applications begins with minimizing the code I use. I focus on the application's functional and non-functional requirements and then create code that satisfies these. I break the application down into distinct processes and code each one sequentially. The final step is to test the application and debug it."
Situational
13. How would you accelerate the response time of a website you created for us here at Facebook?
How to Answer
When conducting an interview, hiring managers like the ones at Facebook are interested in one of three things - how you can help their organization make money, save money, or save time. The questions they ask will be specific to these objectives. You can prepare for the interview by understanding the organization's mission, the role of the job you are interviewing for, and how you can help them achieve one of these three objectives. In this case, the interviewer is seeking to understand how you can save time.
Answer Example
"There are several ways you can accelerate the response time of a website. These include using adaptive images, employing a cache, minimizing the number of plugins you use, compressing the content, and enabling HTTP to keep-alive response headers. The methods I use depend on the specific application and how the users interact with it."
Situational
14. Can you describe a tough software development problem you encountered in your last job and discuss how you solved it?
How to Answer
This is an experience-based question. Experience-based questions ask about a specific situation and seek to understand how you resolved it. This provides the Facebook interviewer with information about your background and your ability to do the job. When responding to this type of question, keep your answer simple using plain language the interviewer is likely to understand.
Answer Example
"When creating an internal application to help our company's employees track their expenses, there was a bug in the program which impacted the rounding of percentages. After hours of examining the application and attempting to fix the problem, I was unable to identify the bug. I asked one of my peers to look at my code, and they quickly found the issue. This helped me realize that sometimes I'm too familiar with the code I write, and a fresh set of eyes can be helpful."
Technical
15. Can you define black box testing and white box testing and discuss the differences between them?
How to Answer
Often during an interview, you are asked to define two terms used in the job and contrast them. This is an example of that type of question. When practicing interview questions, you'll note that your response is typically structured in a specific way. This makes responding to questions during the interview easier because you don't have to think about how to structure your answer. In this case, you want to first define each term and then describe the differences between them. You may also want to provide an example of how the concepts are used and the work you do.
Answer Example
"There are two major types of software testing. These include black box and white box. Black box testing is done without the tester knowing anything about how the application was created. On the other hand, white box testing is done by somebody who is intimately familiar with the structure and content of the application. White box testing allows the tester to examine the code and modify it to fix any issues they discover. Black box testing is typically used to simulate how the user views and interacts with the application."
Technical
16. What are the differences between an array and a stack?
How to Answer
This technical question is asking you to compare two concepts used in the role of a Facebook software engineer. When comparing two concepts, you should first define each of them and then discuss how they differ. It may be helpful if you provide examples of how the concepts are used and the work you do to demonstrate your understanding of the subject matter.
Answer Example
"A stack is a data structure that utilizes the last in, first out principle for presenting data to the application. On the other hand, an array doesn't have a fixed structure for how data is added or retrieved by the application. A stack may be used in an application that requires the most recent data to be presented first. An array can be used to retrieve any of the data, regardless of when it was added to the application."
Technical
17. Facebook web developers are incorporating HTML5 in their most recent websites. Can you describe the functions of web workers in HTML5?
How to Answer
When interviewing for a software engineering position at Facebook, the interviewer will ask various types of technical questions. These can range from very simple to very complex. Typically, the interviewer will start with simpler questions and progress to more complex ones. This indicates they are gaining confidence in your ability to do the job and are willing to explore your background in more detail. Regardless of their complexity, technical questions should always be answered briefly and to the point. You should anticipate follow-up questions any time you provide an answer to the interviewer.
Answer Example
"While JavaScript is widely used when creating web sites, it has its limitations. The language is single-threaded; therefore, concurrent or simultaneous operations are difficult to program. Web workers in HTML5 allow programmers to create scripts that run in the background and are invisible to the users. This is a workaround to executing multi-threaded application operations within JavaScript."
Technical
18. What are the differences between blocking and non-blocking calls in the context of Node.js?
How to Answer
During an interview as a software engineer, you can anticipate that most questions will be technical or operational. The best way to prepare for this type of interview is to first conduct research on the company to understand the type of programming they do and the products they produce. Next, you should carefully review the processes you use as a software engineer to develop programs. Having a clear understanding of these will help you respond to any question the interviewer may ask.
Answer Example
"Blocking calls require that the program waits until a non-JavaScript operation is completed before additional JavaScript commands can be executed. Non-blocking calls can execute commands asynchronously at any time. This characteristic results in non-blocking calls having a performance advantage. Node.js uses both of these types of calls."
Technical
19. What are some of the programming languages you are familiar with, and which ones do you prefer?
How to Answer
This is a general question that an interviewer at Facebook will ask to determine your proficiency in programming, and whether the languages you prefer are the same ones Facebook uses. During an interview, you will be asked a mix of general, operational, technical, and behavioral questions. Interviewers will ask these in random order, so you need to be prepared for each type of question.
Answer Example
"I'm familiar with many different software programming languages. These include C, C++, Java, Ruby, and Perl. My favorite is Ruby because it is easy to use, has a wide range of libraries already available, and is understood by most other programming professionals."
Technical
20. Please describe a stack and the two operations it performs.
How to Answer
When the Facebook interviewer asks you to describe something, you should immediately identify the question as being technical. When responding to a technical question, you first define the term or concept and then describe how it is used in the work you are performing. If the interviewer asks you follow-up questions, they are expressing a strong interest in this topic and indicating that it is important to their operations. This is a signal for you to expand on your answer and give them more details than you normally would.
Answer Example
"A stack is a data structure that has several distinct characteristics. Stacks use a LIFO process, organizing the data as last in, first out. This differs from a queue, which processes data as first-in, first-out. The two operations a stack performs are push, which is insertion of the data at the top of the stack, and pop, which is removal of the last item added to the stack."
Technical
21. Please describe responsive design and the difference between fixed and fluid layouts.
How to Answer
You should immediately recognize this is a technical question. Technical questions ask you to define a term or concept and then discuss how it is used in your work. When responding to this question, you should be brief and to the point. The interviewer at Facebook will request additional information if they need it. You should also provide an example if possible to further demonstrate your knowledge of the subject.
Answer Example
"Responsive design refers to the process of creating web content that is formatted according to the device you are using to browse the site. It uses media queries to address breakpoints and scale images, wrap text, and adjust the layout so that the website is presented consistently across different devices. Compatible devices include computers, tablets, and mobile phones. Response designs utilize the fluid website design process. This differs from a fixed design in that it uses percentages versus fixed pixel widths."
Technical
22. Here at Facebook, we have embraced Agile methodology. How experienced are you with the Agile software development process?
How to Answer
This question is asking about your familiarity with a specific process used in software development. It may be a follow-up question to a previous answer you provided the interviewer. When asked this type of question, you should first define the concept or topic and then explain how it is used in your job. This will demonstrate your knowledge of the subject and your experience employing it in the work you do.
Answer Example
"I am very experienced with the Agile software development process. As you know, it is a methodology used when creating a program. Its central concept is iterative development. This involves collaboration between the software development team and the parts of the organization that will be using the application. The benefit of this is it allows for identifying and correcting issues at each stage of the process rather than after all the work is completed."
Technical
23. Can you describe Facebook's software development life cycle, as you understand it?
How to Answer
This is an example of a hybrid operational and technical question. It asks you to define a concept relative to this profession and describe how you go about doing this job. When answering these types of questions, you should be direct and to the point. The Facebook interviewer is likely to ask several follow-up questions to explore this topic in more detail. Your answer should also be aligned with the requirements for this job, as defined in the job posting.
Answer Example
"The software development life cycle, or SDLC, is a process that most developers follow to create an application or program. The individual steps I understand Facebook uses include defining the requirements, planning the development, creating the code, testing it, and deploying the application. Specific methodologies used to accomplish this include the waterfall or spiral models, or the Agile framework. Is this accurate?"
Technical
24. What do you look for or check when reviewing another team member's code?
How to Answer
This is a hybrid question, which has elements of both operational and technical questions. Since both operational and technical questions are responded to directly and succinctly, your answer should be the same. This question's broad nature also indicates that the interviewer will likely ask a follow-up question regardless of how you respond to their original question.
Answer Example
"When I'm asked to review another team member's code, the first thing I look for is to make sure that the code is efficient and follows our organization's guidelines. I'm careful not to personalize my review or make recommendations on how they could improve the code based on my personal preferences and coding style. I also strive to impart new knowledge to the coder when I make suggestions. An example of this would be showing them a more efficient way to accomplish the task, which they may not have considered."
Technical Engineer
25. What do you feel are the critical principles of good software engineering?
How to Answer
This is a general question that asks you to characterize what makes a software program efficient and effective. Your ability to do this will help the interviewer at Facebook understand your qualifications for the position. Your answer should incorporate both the requirements for the job, as stated in the job description, and your previous experience writing code. You should limit your answer to two to three important principles and anticipate a follow-up question from the interviewer.
Answer Example
"There are several critical principles I try to incorporate in any code I write. These include simplicity, standardization, and ease of understanding. By doing this, I ensure that the code is effective and easy to understand and update, if necessary. I also document my code so that other programmers can comprehend it and modify it if required to do so. Are these the same practices you employ here at Facebook?"
Technical Engineer
26. How would you go about explaining Facebook's cloud computing environment to someone who doesn't have a technical background?
How to Answer
The purpose of this question is to gain an understanding of your communication skills. Throughout the interview, the hiring manager will seek to understand some of the soft skills you have that pertain to this job. These include communication, teamwork, conflict resolution, and others. Every time you answer a question, you are being evaluated for both your experience and skills as well as your ability to communicate. This question relates directly to this objective.
Answer Example
"The easiest way to understand Facebook's cloud is that it is just another version of the computer, Android phone, or Facebook storage device that is located remotely. It is similar to your hard drive or USB drive, except you access it via the Internet instead of directly on your computer. The Facebook cloud can also host applications and execute them remotely. Again, this is similar to your computer, cell phone, or any other device you may use. Whenever you make a phone call, ask Facebook for information, or order something in the Facebook Marketplace, you are using Facebook's cloud."