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| # 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`. | |