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

JSON Data Types — Interview Questions

Reviewed by Gurusankar M.

Asked inInfosysTCSAccentureWipro
#json#data types#string#number#boolean#null
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Short Answer

JSON supports six value types: string (double-quoted), number, boolean (true/false), null, object ({}), and array ([]). It has no date, integer-vs-float distinction, undefined, function, or comment types — dates are usually sent as ISO-8601 strings and big/precise numbers as strings.

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Concept Made Simple

Coffee Chat Question

“What data types does JSON support?”

Remember It Faster

Mind Map Answer

Primitives
string, number, boolean, null
Structured
object {}, array []
No
date, undefined, function, comment
Strings
must use double quotes

Learn by Doing

Hands-on Keyboard

json
{
  "name": "Guru",
  "age": 30,
  "verified": true,
  "manager": null,
  "skills": ["Java", "AWS"],
  "joined": "2026-08-01T09:00:00Z"
}

Think Beyond the Expected

What If?

How do you represent a date, since JSON has no date type?

Use a string, almost always ISO-8601 ("2026-08-01T09:00:00Z"), and parse it on each side (new Date(str) in JS, java.time.Instant in Java). Some teams send a Unix epoch number instead. There's no native date, so both parties must agree on the string/number convention.

Real World

The 'JSON has no date' fact bites everyone eventually — you JSON.stringify a Date and it becomes an ISO string, then forget to parse it back and end up comparing a string to a Date. Money and IDs are often sent as strings to avoid float precision loss.

Interviewer's Expectation

Keywords they're listening for:

  • string/number/boolean/null
  • object & array
  • no date/undefined/function
  • double-quoted strings
  • dates as ISO strings

Common Mistakes

  • Expecting a native date type
  • Using single quotes for strings
  • Assuming numbers keep exact precision (float issues)

Best Practices

  • Send dates as ISO-8601 strings
  • Send money/large IDs as strings to avoid float errors
  • Distinguish null (known-empty) from a missing key

Follow-up Questions

  1. Why send large numbers or money as strings?
  2. How is null different from an absent key?
  3. What happens to undefined during JSON.stringify?

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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: Syntax (JSON)
Interview question: "What data types does JSON support?"

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.
Open inChatGPTGeminiClaude

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