EasyExperience level: 0-2 years · 3-5 years1 min read

Serialization vs Deserialization — Interview Questions

Reviewed by Gurusankar M.

Asked inInfosysTCSAmazonDeloitte
#json#serialization#deserialization#stringify#parse
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Short Answer

Serialization turns an in-memory object into a JSON string (JSON.stringify, json.dumps) for storage or transmission; deserialization does the reverse, turning a JSON string back into objects (JSON.parse, json.loads). Serialize on the way out, deserialize on the way in.

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Concept Made Simple

Coffee Chat Question

“What is the difference between serialization and deserialization?”

Remember It Faster

Mind Map Answer

Serialize
object → JSON string (stringify/dumps)
Deserialize
JSON string → object (parse/loads)
When
serialize to send/store, deserialize to read
Watch
dates, undefined, functions drop/convert

Learn by Doing

Hands-on Keyboard

javascript
const obj = { id: 1, when: new Date("2026-08-01"), fn: () => 1 };

const text = JSON.stringify(obj);   // serialize
console.log(text);
// {"id":1,"when":"2026-08-01T00:00:00.000Z"}  (fn is dropped!)

const back = JSON.parse(text);      // deserialize
console.log(typeof back.when);      // "string" — not a Date

Think Beyond the Expected

What If?

What happens to a Date, a function, and undefined during JSON.stringify?

A Date becomes its ISO string (and won't turn back into a Date on parse), while functions, undefined values, and symbols are omitted from objects (and become null inside arrays). That asymmetry is why round-tripping isn't lossless — you often need a reviver on parse or a toJSON/DTO on serialize.

Real World

The 'my date is now a string' bug comes straight from this: you stringify an object with a Date, send it, parse it, and the field is a string. Teams add reviver functions or map to DTOs to restore types after deserialization.

Interviewer's Expectation

Keywords they're listening for:

  • serialize = object→string
  • deserialize = string→object
  • stringify/parse, dumps/loads
  • lossy for date/undefined/function
  • reviver/replacer

Common Mistakes

  • Expecting a lossless round-trip for dates
  • Forgetting functions/undefined are dropped
  • Confusing which direction is which

Best Practices

  • Use a reviver/DTO to restore types
  • Send dates as ISO strings deliberately
  • Keep serializable objects plain (no functions)

Follow-up Questions

  1. What do the replacer and reviver arguments do?
  2. How do you preserve types across a round-trip?
  3. How do Jackson/Gson map JSON to typed classes?

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Plain-language foundations

I'm preparing for a software engineering interview and want to understand this from scratch, as a beginner.

Topic: Serialization (JSON)
Interview question: "What is the difference between serialization and deserialization?"

Please:
1. Explain the core idea in simple, plain language, using an everyday analogy.
2. Define any technical terms you use.
3. Walk through one small, concrete example.
4. Finish with a single sentence I can easily remember.

Keep the tone friendly and assume I'm new to this topic.
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