96 lines
3.3 KiB
Markdown
96 lines
3.3 KiB
Markdown
# json-parse-even-better-errors
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[`json-parse-even-better-errors`](https://github.com/npm/json-parse-even-better-errors)
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is a Node.js library for getting nicer errors out of `JSON.parse()`,
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including context and position of the parse errors.
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It also preserves the newline and indentation styles of the JSON data, by
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putting them in the object or array in the `Symbol.for('indent')` and
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`Symbol.for('newline')` properties.
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## Install
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`$ npm install --save json-parse-even-better-errors`
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## Table of Contents
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* [Example](#example)
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* [Features](#features)
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* [Contributing](#contributing)
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* [API](#api)
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* [`parse`](#parse)
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### Example
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```javascript
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const parseJson = require('json-parse-even-better-errors')
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parseJson('"foo"') // returns the string 'foo'
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parseJson('garbage') // more useful error message
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parseJson.noExceptions('garbage') // returns undefined
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```
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### Features
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* Like JSON.parse, but the errors are better.
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* Strips a leading byte-order-mark that you sometimes get reading files.
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* Has a `noExceptions` method that returns undefined rather than throwing.
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* Attaches the newline character(s) used to the `Symbol.for('newline')`
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property on objects and arrays.
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* Attaches the indentation character(s) used to the `Symbol.for('indent')`
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property on objects and arrays.
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## Indentation
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To preserve indentation when the file is saved back to disk, use
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`data[Symbol.for('indent')]` as the third argument to `JSON.stringify`, and
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if you want to preserve windows `\r\n` newlines, replace the `\n` chars in
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the string with `data[Symbol.for('newline')]`.
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For example:
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```js
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const txt = await readFile('./package.json', 'utf8')
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const data = parseJsonEvenBetterErrors(txt)
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const indent = Symbol.for('indent')
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const newline = Symbol.for('newline')
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// .. do some stuff to the data ..
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const string = JSON.stringify(data, null, data[indent]) + '\n'
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const eolFixed = data[newline] === '\n' ? string
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: string.replace(/\n/g, data[newline])
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await writeFile('./package.json', eolFixed)
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```
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Indentation is determined by looking at the whitespace between the initial
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`{` and `[` and the character that follows it. If you have lots of weird
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inconsistent indentation, then it won't track that or give you any way to
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preserve it. Whether this is a bug or a feature is debatable ;)
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### API
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#### <a name="parse"></a> `parse(txt, reviver = null, context = 20)`
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Works just like `JSON.parse`, but will include a bit more information when
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an error happens, and attaches a `Symbol.for('indent')` and
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`Symbol.for('newline')` on objects and arrays. This throws a
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`JSONParseError`.
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#### <a name="parse"></a> `parse.noExceptions(txt, reviver = null)`
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Works just like `JSON.parse`, but will return `undefined` rather than
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throwing an error.
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#### <a name="jsonparseerror"></a> `class JSONParseError(er, text, context = 20, caller = null)`
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Extends the JavaScript `SyntaxError` class to parse the message and provide
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better metadata.
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Pass in the error thrown by the built-in `JSON.parse`, and the text being
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parsed, and it'll parse out the bits needed to be helpful.
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`context` defaults to 20.
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Set a `caller` function to trim internal implementation details out of the
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stack trace. When calling `parseJson`, this is set to the `parseJson`
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function. If not set, then the constructor defaults to itself, so the
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stack trace will point to the spot where you call `new JSONParseError`.
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