| # json-parse-even-better-errors |
| |
| [`json-parse-even-better-errors`](https://github.com/npm/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](#example) |
| * [Features](#features) |
| * [Contributing](#contributing) |
| * [API](#api) |
| * [`parse`](#parse) |
| |
| ### Example |
| |
| ```javascript |
| 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`, and |
| if you want to preserve windows `\r\n` newlines, replace the `\n` chars in |
| the string with `data[Symbol.for('newline')]`. |
| |
| For example: |
| |
| ```js |
| 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> `parse(txt, reviver = null, context = 20)` |
| |
| 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> `parse.noExceptions(txt, reviver = null)` |
| |
| Works just like `JSON.parse`, but will return `undefined` rather than |
| throwing an error. |
| |
| #### <a name="jsonparseerror"></a> `class JSONParseError(er, text, context = 20, caller = null)` |
| |
| 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`. |