nr-json5

A JSON5 reader and a canonical single-line writer, with no dependencies and nothing else in the box.

import { parseJson5, stringifyJson5 } from '@notrealstudio/nr-json5'

parseJson5("{ model: 'gpt-4o', /* trailing commas fine */ steps: 30, }")
// → { model: 'gpt-4o', steps: 30 }

stringifyJson5({ model: 'gpt-4o', steps: 30 })
// → "{model: 'gpt-4o', steps: 30}"

The reader is a port of the reference implementation (json5 2.2.3, MIT) — the same state machine, so the official json5-tests suite stays green: comments, unquoted keys, single quotes, trailing commas, hex, leading and trailing decimal points, +/-, Infinity, NaN, escaped and multi-line strings. Two deliberate departures: identifier and space character classes use Unicode property escapes instead of the reference's 15 KB of tables frozen at Unicode 9, and there is no reviver — parser state is per-instance rather than module-global.

The writer is not a port. It emits canonical relaxed JSON5 on one line: bare keys where the key is an ASCII identifier, single-quoted strings, one space after : and ,, no trailing comma. Deterministic — two callers emit identical bytes, which is what makes it safe to diff, to compare, and to embed in a line-oriented format. It mirrors JSON semantics for toJSON, and for undefined, functions and symbols (dropped from objects, null inside arrays); it throws a TypeError on a circular structure, on a BigInt, and on a top-level value with no JSON5 representation.

Install

npm install @notrealstudio/nr-json5

Zero dependencies, no host APIs — Node, browsers, Google Apps Script, userscripts, anywhere with a modern JS engine. A parse error is a SyntaxError carrying lineNumber and columnNumber, so you can point at the offending character.

License

MIT. The reader derives from json5 (c) 2012-2018 Aseem Kishore and others, also MIT.