Parsing #1 — Building a Simple JSON.stringify()

JSON.stringify() converts JavaScript values to JSON text. Behind its simple API, it handles objects, arrays, primitives, nested structures, and circular references. This article builds a simplified but functional stringify from scratch.

Prerequisites: Recursion Patterns

1. What JSON.stringify() Handles

JSON supports: objects, arrays, strings, numbers, booleans, and null. It rejects: functions, undefined, Symbols, BigInt, and circular references:

2. Basic stringify — Primitives, Objects, Arrays

3. Circular Reference Detection

4. The toJSON() Method — Custom Serialization

If an object has a toJSON() method, JSON.stringify() calls it:

5. The replacer Parameter — Filter and Transform

Accepts an array of keys or a transformer function:

6. Building a Minimal JSON.parse() (Bonus)

JSON parsing is significantly more complex (requires a real parser). Here's a conceptual overview:

Key Takeaways

• JSON.stringify() handles primitives, objects, arrays, null — skips functions and undefined.
• Escape strings properly: ", \\, \n, \r, \t.
• NaN and Infinity become null in JSON.
• Circular references throw TypeError — use a WeakSet to detect them.
• toJSON() lets objects customize serialization.
• replacer (array or function) filters/transforms during serialization.

Next: Parsing #2 — URL & Query String Parsing — parse query strings into objects and build them back.