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Series B+ Startup·Software Engineer·Technical Phone Screen·Senior

SeniorPrefer not to say
Jun 2026

Summary

Went for a lead developer role and the technical portion leaned hard into SOLID principles, polymorphism, and design patterns. Knew enough to get by but not enough to sound confident, which is a bad place to be in a lead interview.

Questions Asked (3)

Q1

Can you explain the SOLID principles and how you apply them in practice?

Technical Trade-offsSystem Design
Author's notes

Knew the acronym, stumbled on the actual explanations.

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AI HintsAI Generated

Suggested Approach

Start by briefly defining each SOLID principle in one sentence, then pivot to a concrete example from your experience where you applied one or more principles to solve a real problem. Emphasize the trade-offs and how you balanced SOLID with pragmatism in a startup environment.

Pro tip: Don't just recite definitions—show how you've used SOLID to reduce technical debt or improve maintainability, and acknowledge that over-applying SOLID can lead to over-engineering, especially in early-stage startups.

1. Define SOLID concisely

Give a one-sentence definition for each principle (SRP, OCP, LSP, ISP, DIP) to show you know the theory, but keep it brief.

2. Share a real-world example

Pick one or two principles and describe a specific project where you applied them, such as refactoring a monolithic class into smaller ones (SRP) or using dependency injection (DIP).

3. Highlight the impact

Explain the positive outcomes: improved testability, reduced coupling, easier onboarding, or faster feature delivery.

4. Discuss trade-offs and pragmatism

Acknowledge that blindly following SOLID can lead to over-abstraction; describe how you decide when to apply principles based on project stage and team needs.

5. Connect to system design

Tie SOLID to broader architectural decisions, such as how it influences module boundaries or microservices decomposition.

Key Points to Mention

  • Single Responsibility Principle (SRP) and how it reduces the risk of unintended side effects
  • Open/Closed Principle (OCP) and its role in extensibility without modifying existing code
  • Liskov Substitution Principle (LSP) and ensuring subclasses don't break client code
  • Interface Segregation Principle (ISP) and avoiding fat interfaces that force unnecessary dependencies
  • Dependency Inversion Principle (DIP) and how it enables testability and decoupling
  • Trade-offs: when to apply SOLID vs. when to keep things simple, especially in a startup context

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.

Q2

How would you describe polymorphism and where does it come up in your work?

Technical Trade-offs
Author's notes

Gave a decent answer but it felt abstract.

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AI HintsAI Generated

Suggested Approach

Start with a clear, concise definition of polymorphism, then immediately connect it to a real example from your work. Emphasize how polymorphism enables flexibility and maintainability, and discuss trade-offs you've considered when applying it.

Pro tip: Show that you understand polymorphism beyond just inheritance—mention interfaces, duck typing, or generics, and how they help manage complexity in a startup environment where requirements change quickly.

1. Define polymorphism clearly

Give a succinct definition: the ability of different types to respond to the same interface or method call, enabling code to work with objects of multiple types.

2. Provide a concrete example

Describe a specific instance from your work where you used polymorphism, such as implementing a payment gateway with multiple providers or handling different file formats.

3. Explain the benefits and trade-offs

Discuss how polymorphism improved extensibility, reduced duplication, or simplified testing, but also mention potential downsides like indirection or performance overhead.

4. Connect to startup context

Relate how polymorphism helps in a fast-paced startup by allowing quick adaptation to new requirements without major refactoring.

5. Summarize impact

Conclude with the overall impact on your team or project, such as increased development speed or easier onboarding.

Key Points to Mention

  • Definition: polymorphism allows objects of different types to be treated as instances of a common supertype or interface.
  • Types: subtype polymorphism (inheritance), parametric polymorphism (generics), ad-hoc polymorphism (overloading).
  • Real-world example: e.g., using a common interface for multiple payment processors or storage backends.
  • Benefits: code reuse, flexibility, easier testing via mocks, and adherence to SOLID principles like Open/Closed.
  • Trade-offs: increased abstraction can make code harder to trace; performance overhead in some languages.
  • Startup relevance: enables rapid iteration and scaling without rewriting core logic.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.

Q3

What React-specific design patterns do you use and how would you explain them to a team?

Technical Trade-offsSystem Design
Author's notes

This is where I felt the gap most.

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AI HintsAI Generated

Suggested Approach

Select 2-3 React patterns you've actually used, explain the problem each solves, and describe how you'd teach them to your team with concrete examples and trade-offs. Emphasize maintainability, scalability, and team alignment over just listing patterns.

Pro tip: Tie each pattern to a real project outcome (e.g., 'We adopted compound components to make our design system more flexible, reducing prop drilling by 40%'). This shows you understand the why, not just the what.

1. Choose Relevant Patterns

Pick 2-3 patterns that are widely applicable and that you have hands-on experience with, such as compound components, render props, higher-order components, or custom hooks.

2. Explain the Problem and Solution

For each pattern, briefly state the problem it addresses (e.g., prop drilling, logic reuse) and how the pattern solves it in a React-idiomatic way.

3. Provide a Concrete Example

Give a short code snippet or describe a real scenario where you applied the pattern, highlighting the benefits and any trade-offs.

4. Describe Team Adoption

Explain how you would introduce the pattern to your team: through documentation, pairing, code reviews, or internal talks, ensuring everyone understands when and why to use it.

5. Discuss Trade-offs and Alternatives

Acknowledge that no pattern is a silver bullet; mention when you might avoid it and what alternatives exist, showing balanced judgment.

Key Points to Mention

  • Compound components (e.g., <Select> and <Option>) for flexible, expressive APIs
  • Custom hooks for reusable stateful logic without changing component hierarchy
  • Render props or higher-order components for cross-cutting concerns (though hooks are often preferred now)
  • Context API for avoiding prop drilling in deeply nested trees
  • The importance of consistency and documentation when teaching patterns to a team
  • Trade-offs: added abstraction vs. simplicity, performance implications, and learning curve

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.