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A module for reading, writing, and manipulating JSON files

Importing the package

import JsonFile from '@exponent/json-file';

Promise-based async API

Everything returns Promises. If you are using ES7 (or Babel), you can write code like this:

let config = await JsonFile.readAsync('config.json', {cantReadFileDefault: {}});

If you are using ES6, you can just use the return values the way you normally would use Promises.

JsonFile.readAsync('config.json', {cantReadFileDefault: {}}).then(config => {

Used as an object

var file = new JsonFile('config.json', {cantReadFileDefault: {}});
var somethingSaved = await file.getAsync('somethingSaved', null);

Used as functions

var pkg = await JsonFile.readAsync('package.json');
var main = await JsonFile.getAsync('package.json', 'main', 'index.js');

Options you can set, and their default values

Option Description Default Value
space How many spaces to use when pretty-printing, (0 for no pretty-printing) 2
default Catch-all default value for missing values, bad JSON, and files that can't be read undefined
jsonParseErrorDefault The default value for when a file is read but it doesn't contain valid JSON undefined
cantReadFileDefault The default value for when a file can't be read undefined
  • Note that if defaults are undefined, then an Error will be thrown instead of undefined being returned



Returns the parse of the whole file as an object

.getAsync(key, [default-value], [options])

Returns a single value from a JSON file, using lodash's _.get to query the whole object.


.writeAsync(data, [options])

Writes out the given data to the file

.setAsync(key, val, [options])

Updates the file, inserting or updating the value for <key> with <val>

.mergeAsync(sources, [options])

Merges the values in <sources> into the object currently encoded in the file.

.deleteKeyAsync(key, [options])

Deletes a single key from the top level of the file.


The functions available all mirror the methods above but take file (filename as a string) as their first argument.