Openai·Software Engineer·Technical Phone Screen·Senior

SeniorPrefer not to say

Jun 2026Remote

Summary

Interviewed for a software engineering role at OpenAI and got a pretty deep coding question around serialization. Not a LeetCode grind session, more of a 'show me you understand how the web and JS actually work' kind of thing.

Questions Asked (2)

Implement a toString utility that can serialize DOM-like node objects (with tag names, attributes, and children) as well as JavaScript functions back into readable string form.

System DesignTechnical Trade-offsAPI & Integrations

Author's notes

The DOM serialization part felt manageable at first.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the requirements and scope: what types of nodes and functions need to be serialized, and what level of fidelity is expected. Then outline a recursive traversal algorithm that handles each node type, with special cases for functions, and discuss trade-offs like handling circular references and performance. Finally, walk through a concrete example to demonstrate the utility.

Pro tip: Mention that you would use a WeakSet to track visited objects to avoid infinite loops on circular references, and discuss how to handle edge cases like functions with closures or native code.

1. Clarify Requirements and Scope

Ask questions to understand the expected input types, output format, and any constraints such as handling circular references or special node types. Confirm whether functions should be serialized as source code or just a placeholder.

2. Design the Recursive Algorithm

Outline a recursive function that processes each node: for elements, output the tag name, attributes, and recursively process children; for text nodes, output the text content; for functions, output the function source or a representation.

3. Handle Edge Cases and Trade-offs

Discuss how to handle circular references using a WeakSet, how to deal with functions that are native or bound, and performance considerations for deep or large trees. Mention potential security concerns if serializing untrusted input.

4. Implement and Test with Examples

Write pseudocode or actual code for the utility, then walk through a sample DOM-like structure and a function to show the output. Test with edge cases like empty nodes, attributes with special characters, and nested functions.

Key Points to Mention

Recursive traversal of the node tree
Handling different node types (element, text, comment, etc.)
Serializing functions using Function.prototype.toString()
Using a WeakSet to detect and handle circular references
Escaping attribute values and text content for valid output
Performance considerations for large trees and potential optimizations

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

How would you handle circular references and bound functions as edge cases in your serialization utility?

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

Circular refs I actually had a decent answer for since I'd seen the JSON.stringify replacer pattern before.

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AI HintsAI Generated

Suggested Approach

Start by acknowledging that circular references and bound functions are common edge cases in serialization, then explain your strategy for detecting and handling them. Emphasize trade-offs between correctness, performance, and simplicity, and mention how you would test these cases.

Pro tip: Mention that bound functions lose their original function identity, so you might serialize them as null or a placeholder, and consider using a WeakSet to track visited objects for circular references to avoid memory leaks.

1. Identify the edge cases

Clearly define what circular references and bound functions are and why they cause issues in serialization (e.g., infinite loops, loss of context).

2. Choose detection strategies

For circular references, use a WeakSet or Map to track visited objects; for bound functions, detect them via Function.prototype.toString or checking for a bound function property.

3. Decide on handling approaches

For circular references, either throw an error, replace with a placeholder, or use a library like flatted; for bound functions, serialize as null, a string representation, or omit them.

4. Discuss trade-offs

Compare approaches in terms of performance, memory usage, and correctness, and justify your choice based on the use case.

5. Outline testing strategy

Describe how you would test these edge cases, such as unit tests with circular objects and bound functions, and ensure no infinite loops occur.

Key Points to Mention

Circular references can cause infinite recursion; use a WeakSet to track visited objects.
Bound functions have a different identity and cannot be serialized directly; consider serializing as null or a placeholder.
Trade-offs: performance overhead of tracking vs. correctness; memory usage of WeakSet vs. Map.
Alternatives: use JSON.stringify with a replacer function, or third-party libraries like flatted or circular-json.
Testing: write unit tests that include circular structures and bound functions to ensure the serializer handles them gracefully.
Documentation: clearly document how your serializer handles these edge cases to set user expectations.

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