Build a JSON Parser from Scratch

"What I cannot create, I do not understand." — Richard Feynman

This repository is a Zero Dependency implementation of a JSON parser in pure JavaScript. It demonstrates how compilers/parsers work under the hood.

How it Works

1. Lexical Analysis (The Lexer)

The Lexer takes a raw string and breaks it into Tokens. Input: {"a": 1} Tokens: LBRACE -> STRING("a") -> COLON -> NUMBER(1) -> RBRACE

2. Syntactic Analysis (The Parser)

The Parser takes the stream of Tokens and builds the AST (Abstract Syntax Tree) or actual Object using Recursive Descent.

// Pseudo-code of Recursive Descent
function parseValue() {
  if (token == LBRACE) return parseObject()
  if (token == LBRACKET) return parseArray()
  if (token == STRING) return token.value
  // ...
}

Quick Start

No npm install required! This is pure Node.js.

# Run the demo
node examples/demo.js

# Run the test suite
node tests/run_tests.js

Features

• [x] Null, Booleans (true/false)
• [x] Strings (with escapes)
• [x] Numbers (Integers/Floats)
• [x] Nested Objects & Arrays
• [x] Zero Dependencies

Why learn this?

Understanding parsing is the key to:

• Writing your own DSLs (Domain Specific Languages).
• Understanding how Babel/ESLint works.
• Crushing System Design interviews.