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json-parse-even-better-errors

`json-parse-even-better-errors` is a Node.js library for getting nicer errors out of `JSON.parse()`, including context and position of the parse errors.

It also preserves the newline and indentation styles of the JSON data, by putting them in the object or array in the ‘Symbol.for('indent’)`and` Symbol.for('newline')` properties.

# Install

`$ npm install --save json-parse-even-better-errors`

# Table of Contents

- Example
- Features
- Contributing
- API
  - `parse`

## Example

const parseJson = require('json-parse-even-better-errors')
parseJson('"foo"') // returns the string 'foo'
parseJson('garbage') // more useful error message
parseJson.noExceptions('garbage') // returns undefined

## Features

- Like JSON.parse, but the errors are better.
- Strips a leading byte-order-mark that you sometimes get reading files.
- Has a `noExceptions` method that returns undefined rather than throwing.
- Attaches the newline character(s) used to the ‘Symbol.for('newline’)` property on objects and arrays.
- Attaches the indentation character(s) used to the ‘Symbol.for('indent’)` property on objects and arrays.

# Indentation

To preserve indentation when the file is saved back to disk, use ‘data[Symbol.for('indent’)]`as the third argument to`JSON.stringify<tt>, and if you want to preserve windows\r
`newlines, replace the`
`chars in the string with`data[Symbol.for('newline')]`.

For example:

const txt = await readFile('./package.json', 'utf8')
const data = parseJsonEvenBetterErrors(txt)
const indent = Symbol.for('indent')
const newline = Symbol.for('newline')
// .. do some stuff to the data ..
const string = JSON.stringify(data, null, data[indent]) + '\n'
const eolFixed = data[newline] === '\n' ? string
: string.replace(/\n/g, data[newline])
await writeFile('./package.json', eolFixed)

Indentation is determined by looking at the whitespace between the initial `{` and `[` and the character that follows it. If you have lots of weird inconsistent indentation, then it won't track that or give you any way to preserve it. Whether this is a bug or a feature is debatable ;)

## API

### <a name="parse"></a> <tt>parse(txt, reviver = null, context = 20)</tt>

Works just like `JSON.parse`, but will include a bit more information when an error happens, and attaches a ‘Symbol.for('indent’)`and` Symbol.for('newline')`on objects and arrays. This throws a` JSONParseError`.

### <a name="parse"></a> <tt>parse.noExceptions(txt, reviver = null)</tt>

Works just like `JSON.parse`, but will return `undefined` rather than throwing an error.

### <a name="jsonparseerror"></a> <tt>class JSONParseError(er, text, context = 20, caller = null)</tt>

Extends the JavaScript `SyntaxError` class to parse the message and provide better metadata.

Pass in the error thrown by the built-in `JSON.parse`, and the text being parsed, and it'll parse out the bits needed to be helpful.

`context` defaults to 20.

Set a `caller` function to trim internal implementation details out of the stack trace. When calling `parseJson`, this is set to the `parseJson` function. If not set, then the constructor defaults to itself, so the stack trace will point to the spot where you call `new JSONParseError`.