JSON Syntax Rules — Interview Questions
⚡ Short Answer
Valid JSON: data is name/value pairs; objects use {}, arrays use []; keys and string values must use double quotes; values are string/number/boolean/null/object/array; items are comma-separated with NO trailing comma; no comments; the whole document is one value. Whitespace between tokens is ignored.
☕Coffee Chat Question
Concept Made Simple
“What are the syntax rules of valid JSON?”
🧠Mind Map Answer
Remember It Faster
⌨️Hands-on Keyboard
Learn by Doing
// ✅ valid
{ "id": 1, "tags": ["a", "b"] }
// ❌ invalid: single quotes, trailing comma, comment
{ 'id': 1, "tags": ["a", "b",], /* note */ }🔥What If?
Think Beyond the Expected
Why does a trailing comma break JSON when JavaScript allows it?
JSON is a strict subset of JavaScript's object syntax and the spec forbids trailing commas, comments, and single quotes to keep parsers simple and unambiguous. JS object literals are more forgiving, but JSON.parse follows the strict grammar — a trailing comma throws a SyntaxError.
😂Real World
The classic 3am bug: someone hand-edits a config file, leaves a trailing comma or a comment, and the whole service fails to boot. Linters and JSON5/JSONC exist precisely because strict JSON is unforgiving of these.
🎯Interviewer's Expectation
Keywords they're listening for:
⚠️Common Mistakes
- ✗Trailing comma after the last item
- ✗Single quotes or unquoted keys
- ✗Adding // or /* */ comments
✅Best Practices
- ✓Lint/validate JSON in CI and editors
- ✓Use JSONC/JSON5 only where the parser supports it
- ✓Never hand-edit critical JSON without validation
🔁Follow-up Questions
- 1What is JSON5 / JSONC and why do they exist?
- 2Can the top level be an array or a primitive?
- 3How do you validate JSON syntax programmatically?
🧩Related Technologies
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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 are the syntax rules of valid JSON?" 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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