A full-stack developer can be a valuable asset to your team. With experience in coding both front-end and back-end applications, full-stack developers are versatile and in demand. Unfortunately, the competition for hiring tech talent is intensely competitive right now. Finding a qualified full-stack engineer can consume a lot of your company's resources. The finding, vetting, and hiring a developer processes are extensive and complicated.
Since full-stack developers are the "jack of all trades" of developers, the good ones have a deep understanding of a range of programming languages and frameworks. Unfortunately, many unqualified developers have a very shallow understanding of these concepts. Asking the right full-stack developer interview questions can help you differentiate between qualified and unqualified candidates so you can choose the best applicant to join your team.
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Entry-Level Full Stack Developer Interview Questions
All full-stack developers should be able to handle server-side scripting and client-side scripting. However, your expectations for entry-level candidates will naturally be lower than for mid- or senior-level developers. Entry-level developers won't be expected to work independently and will be mentored by more senior developers on their team.
In a junior-level full-stack developer, you should look for familiarity and basic-level competence rather than expertise in the following areas:
- Database technologies such as MySQL, Oracle, and MongoDB
- HTML and CSS
- Backend frameworks such as Ruby on Rails, Django, and NodeJS
- Other skills such as machine learning, Git, SSH, data structures, character encoding, and Linux commands
You'll also want to ensure your prospects have excellent written and oral communication skills, attention to detail, and problem-solving skills. Here are some questions you can ask entry-level candidates to assess their skill level:
What does a full-stack developer do?
You want to ensure your applicant truly understands the type of work they're expected to do. Obviously, the specifics will vary depending on the job, but they should know the general types of tasks they'll need to do. Full-stack developers are responsible for both client-side and server-side applications. They need to understand all of the web development components in order to program for browsers, databases, and servers. A full-stack engineer should understand the job duties associated with all of these tasks.
What are your favorite languages to develop with and why?
Full-stack developers work with a variety of languages, so they should be able to discuss the benefits of more than one language. If they can only discuss one, that's a red flag. Look for candidates who can talk about the benefits and drawbacks of several languages, including the most common front-end languages and back-end languages. They should be familiar with the most common languages, such as HTML, CSS, and Python.
What makes a good full-stack developer?
This question will allow you to evaluate your candidate's understanding of the qualities of a good full-stack developer. Look for a candidate who discussed the importance of deep knowledge of a full range of front and back programming languages that can cover almost any web application. They should also talk about the importance of working within a team environment and effectively communicating with both tech and nontech audiences. Software developers need to be able to understand and communicate with stakeholders at all levels.
How do you keep abreast of the latest industry trends?
In the process of a full-stack developer interview, you want to evaluate whether the candidate embraces the concept of lifelong learning. Industry trends change rapidly. Since 2017, 1 in 3 tech skills has become obsolete, so developers will need to continue learning throughout their careers. People who are relieved to be finished with school and have no curiosity or desire to learn new technologies aren't good candidates for tech careers. Good answers for this question include recent classes they've taken, webinars they've attended, or forums they participate in.
What's the most recent thing you've learned?
Asking what they've learned recently from their favorite source will help you determine if they were being sincere with their previous answer. Consider it a warning sign if they can't easily name something they learned within the past month or so. Keeping up with the industry trends is essential for a developer, particularly a generalist like a full-stack developer.
Explain pair programming
Pair programming is a common agile development technique where two software engineers work on the same terminal together. It holds the core elements of extreme programming. The two programmers should be equally skilled, with one working as the driver and the other as the navigator. They design, code, and test user stories. The navigator guides the general direction of the programming efforts while the driver does the programming. This technique requires a lot of collaboration and communication between the two developers. Pair programming isn't ideal for every situation, but programmers should be familiar with the technique since it can be a powerful method for development. Additionally, pair programming requires a solid grasp of both hard and soft skills that full-stack developers need.
What is cross-origin resource sharing (CORS)?
CORS allows web scripts that run on browser clients to access web resources on different domains. This results in better integration between web services. Without a CORS policy, an app that needs to access resources from another domain will be blocked by the single-origin policy (SOP). CORS will circumvent these restrictions.
Midlevel Full Stack Developer Interview Questions
You'll expect midlevel full-stack developers to have a stronger grasp of technical skills and several years of development experience under their belts. You want someone who is a team player and can contribute without as much hand-holding as an entry-level full-stack developer. They should be able to talk about the projects they've participated in and what they've contributed to them. Look for signs that they have the initiative to work independently while still performing within a team. They should have deep knowledge of the different methods of working on the presentation, business logic, and database layers.
However, it's important to keep in mind that you don't expect the same level of skill from a midlevel developer as you would from a senior-level developer. Midlevel developers can be responsible for aspects of a project, but you wouldn't expect them to handle the entire project alone. They can also help mentor junior-level developers, although they should continue to be mentored by developers with more experience. Here are some interview questions and answers you can ask to judge the competence of a midlevel developer:
What is the Pyramid of Doom?
Asynchronous programming code — when multiple functions are running at the same time — often develops an anti-pattern where there are many nested "if" statements or functions. Because these functions depend on one another, the end result is a tangled mess of multiple callback functions that are difficult to read or maintain. This makes it difficult to determine the flow of the application and perform effective debugging.
Walk me through a project you've worked on, including the technologies you used and why you made those choices
Since midlevel applicants should have plenty of hands-on experience working on real-world problems, they should be able to answer this question easily. Asking them to detail projects they've worked on will demonstrate their expertise with languages and frameworks and highlight their understanding of which technology they should use for a particular application. For a full-stack developer, languages, frameworks, and databases are tools that are used to solve specific problems. The more tools they know, the more choices they have, and the better they can solve specific problems.
You can also use this question to better understand the candidate's problem-solving ability and ability to collaborate with others. Listen to how they describe the contributions. While you want them to demonstrate their skills and abilities, you should also look for signs that they downplay others' contributions.
DevOps is an agile development concept that integrates processes and collaboration between development and IT teams. It aims to speed up the software development life cycle to improve the products and, ultimately, customer satisfaction with the products. DevSecOps takes this notion a step further, making security a part of the process from day one. Instead of tacking on security as an afterthought, a DevSecOps approach makes security everyone's responsibility throughout the software development lifecycle. Any security concerns are addressed as soon as they're raised.
Cybersecurity attacks have increased 37% between the second and third quarters of 2022, according to Statista. Security is an increasing concern for all organizations. You want a full-stack software developer who will approach every project with a security mindset. They should be able to explain the role of code security and application security and how they can follow best practices that include zero trust principles and perimeterless security. With most applications running on the cloud and the increase in remote access, security needs to be top of mind for everyone, particularly midlevel developers with experience.
What is dependency injection?
Dependency injection is a design pattern that allows you to implement the Inversion of Control (IoC). With dependency injection, you can create dependent objects outside of classes so they can be made available to classes differently. Dependency injection includes the following three classes:
- A client class that depends on a server class
- A server class that provides services to a client class
- An injector class that injects objects from the server class into a client class
What is REST?
REST stands for representational state transfer. A REST API is a type of architectural style for an API that manages information with HTTP requests. This can be used with the following functions on data types:
What projects are you currently working on?
A developer should always be working on something and be excited to talk about it. Whether it's a project at their current job or a passion project they're pursuing independently, a good candidate should be able to discuss in detail (outside of confidential information, of course) what they're coding currently. While it doesn't matter what they're working on, this question should give a candidate the chance to demonstrate their enthusiasm and working process.
What is the difference between server-side scripting and client-side scripting?
Although even a junior-level developer should be able to answer this question, a mid-level full-stack developer should be able to go into a deeper explanation beyond just a definition. They should also explain the security and processing statuses for each.
Server-side scripting is done on the back end. It's far more secure than client-side scripting, and the users can't view the scripts. The back end has to interact with servers and uses languages such as Ruby on Rails, PHP, Python, and ColdFusion.
Senior-Level Full Stack Developer Interview Questions
A senior-level full-stack developer can handle the end-to-end software development lifecycle. They will oversee analyzing stakeholder needs, coding, building, testing, and deploying software applications. They will be responsible for assigning work, mentoring midlevel developers, and assigning mid-level developers to mentor junior developers. When you're interviewing senior developers, you are just as interested in their leadership skills as you are in their technical skills.
Senior developers will have a lot more responsibility and will lead teams in addition to contributing to the teams. These developers have many years of experience working on projects, so their technical skills should be very well developed. You can expect them to have a broad and deep knowledge of many languages and frameworks. They should be able to solve the most complex problems and demonstrate the ability to see a project through all phases, from conception to deployment.
You can gain the best understanding of a senior-level developer's suitability for the job by asking them about their past experiences and how they've handled previous projects.
What is your biggest mistake in your career, and what steps did you take to correct it?
Mistakes are a part of the work process for developers. The goal for development isn't the absence of failure. Instead, the goal is to fail fast, recover, and address the problems early. Developers fail constantly, so they need to know how to recover and move on from failure. Listening to your candidate talk about their mistakes will give you a chance to see how they handle failure and how they work with others under stress. Look for signs they can accept criticism without getting defensive and can work well with others without blaming them.
How can you optimize a website for speed and scalability?
A senior developer should be able to elegantly design websites to optimize speed and scalability. Some of the methods they should mention for reaching this goal include:
- Optimizing assets
- Serving scaled images
- Reducing DNS lookups
- Specifying image dimensions
- Leveraging browser caching
- Minimizing request size
- Avoiding duplicate code
- Enabling zipping
Explain the different types of design patterns
Design patterns are repeatable solutions for problems that tend to crop up frequently in software development. They revolve around relationships between objects and classes. The three main types of design patterns are:
- Behavioral patterns that outline object communication patterns, including object-creational patterns and class-creational patterns
- Structural patterns that reorganize objects and classes to form larger and new functionalities
- Creational patterns that concern class instantiation or object creation
When have you discovered a colleague's flawed code, and how did you handle it?
A full-stack developer with years of experience has undoubtedly both produced and discovered bad code. That's part of the process of programming. A senior candidate should be able to handle finding flawed code and bringing it to a colleague's attention with tact and diplomacy. Ideally, they'll use this as an opportunity to mentor a junior-level developer so they can learn from it. You want a candidate who is invested in their team's growth and development as well as their own.
Tell me about your best implementation or debugging experience
This question will give your interviewee a chance to shine and display their skills without feeling like they're bragging. Additionally, it will give you a good idea of the complexity of their past projects as well as what they consider creative problem-solving techniques. With this question, you may discover an otherwise lackluster candidate has analytical and creative thinking skills that weren't apparent earlier. You may also discover that a candidate with an impressive resume doesn't have as much depth and complexity of thought as you assumed.
Next Steps in Hiring Full-Stack Software Engineers
When you're looking to hire full-stack developers, working with a talent partner such as Revelo can simplify the process and make your job easier. We help you find, hire, and pay top-notch engineering talent from Latin America. Our pre-vetted pool of highly qualified software developers speak English fluently and work in times zones that are near U.S. time zones.
Our end-to-end staffing solution gives you a competitive advantage in today's highly competitive tech labor market. Reach out today to find out how we can help you with hiring, HR, payroll, benefits, taxes, and local compliance.