json5-trueformat

json5-trueformat is a TypeScript library for parsing, editing, and serializing JSON and JSON5 files without losing formatting details. It creates a custom AST that captures every comment, blank line, indentation, and other formatting details to ensure a lossless round-trip.

This library is inspired by the design of xml-trueformat and is ideal for use cases where the exact layout and comment structure of JSON files must be preserved (e.g., configuration files under version control). Enjoy seamless, non-destructive editing of your JSON files!

Features

• Exact Formatting Preservation
  Retains inline comments, blank lines, and all whitespace exactly as in the original file.

• AST-based Editing
  Provides an abstract syntax tree for precise modifications. Change the value of a key or add new entries without reformatting the rest of the file.

• Modifications
  Supports adding, removing, and updating keys and values in JSON5 objects and arrays. Convenient methods are provided to simplify adding entries matching the surrounding formatting.
  See e.g. JSON5Object.addKeyValue(key, value, options).

• Support for Comments and Whitespace
  Captures and preserves comments and whitespace within objects and arrays.
  See JSON5ObjectEntry and JSON5ArrayElement.

Installation

Install the dependencies:

npm install json5-trueformat

Usage

Below is an example that reads a JSON5 file, updates a value, and writes it back without changing the formatting:

import { parseJSON5, JSON5Document, JSON5Object, JSON5ObjectEntry, JSON5Literal } from 'json5-trueformat';

const input = `{
  // This is a comment
  key_without_quotes : "value with qutes",
  "key_with_quotes":'value with single quotes',
}`;

const doc = parseJSON5(input);

// expeted AST:
expect(doc).toEqual(
  new JSON5Document(
    '',
    new JSON5Object([
      '\n  // This is a comment\n  ',
      new JSON5ObjectEntry('', 'key_without_quotes', ' ', ' ', new JSON5Literal('value with qutes', '"'), '  ', ','),
      '\n  ',
      new JSON5ObjectEntry('"', 'key_with_quotes', '', '', new JSON5Literal('value with single quotes', "'"), '', ','),
      '\n',
    ]),
    '',
  ),
);

// modify the value of a key:
(doc.value as JSON5Object).entries.find((e) => e instanceof JSON5ObjectEntry)!.value.raw = 'new value';

// add a new key-value pair:
(doc.value as JSON5Object).addKeyValue('new_key', new JSON5Literal('new value', '"'));

// expect serialization to preserve the formatting:
expect(doc.toString()).toEqual(`{
  // This is a comment
  key_without_quotes: "new value",
  "key_with_quotes": 'value with single quotes',
  "new_key": "new value",
}`);

Contributing

Contributions, bug reports, and feature requests are welcome!

Please open an issue or submit a pull request on the GitHub repository.