Deepmerge Json

A simple library to deep merge json files with array operations. Hugely inspired by the awesome deepmerge project.

Note that you can use to merge javascript objects, but the main reason this library was created was to merge json files with optional special operations for array merging.

let left = {
  keep: 'keep',
  simple: 10,
  obj: { a: { multi: { level: 'property' } }, is: 'ok' },
  merge: [0, 1, 2, 3],
  append: [0, 1, 2],
  prepend: [0, 1, 2]
};

let right = {
  simple: 20,
  obj: { a: { multi: { level: 'and' }, deep: 'property' } },
  merge: [10, 20],
  append: { $append: [3, 4, 5] },
  prepend: { $prepend: [-2, -1] }
};

let result = merge(left, right);
console.log(result);

// Result
{
  keep: 'keep',
  simple: 20,
  obj: { a: { multi: { level: 'and' }, deep: 'property' }, is: 'ok' },
  merge: [10, 20, 2, 3],
  append: [0, 1, 2, 3, 4, 5],
  prepend: [-2, -1, 0, 1, 2]
}

Explanation: it deeply merges right object into left without altering them and their properties. Everything is cloned. Arrays elements are merged based on right parameters passed as objects.

Installation

With NPM

npm install deepmerge-json

After that you can import it:

import merge from 'deepmerge-json';

or

const merge = require('deepmerge-json');

There is even a Typescript d.ts definition file to support auto complete.

With a CDN

Just add this line to your HTML file:

<script src="https://unpkg.com/deepmerge-json@latest/dist/deepmerge-json.min.js></script>

Usage

The main reason this library was created was to mimic and extend some array merging functions from mongodb when merging two sets of properties json files.

Simple merge

It is possible to merge recursively all types of properties.

const left = {
  boolValue: false,
  numberValue: 100,
  stringValue: 'target',
  objectValue: {
    foo: 0,
    bar: 'bar',
    baz: {
      baz1: 1,
      baz2: 2
    }
  }
};

const right = {
  boolValue: true,
  numberValue: 222,
  stringValue: 'source',
  objectValue: {
    foo: 'foo',
    baz: {
      baz3: 3
    }
  }
};

const res = merge(left, right);

// result
{ 
  boolValue: true,
  numberValue: 222,
  stringValue: 'source',
  objectValue: {
    foo: 'foo',
    bar: 'bar',
    baz: {
      baz1: 1,
      baz2: 2,
      baz3: 3
    }
  }
}

Array merge

Merging arrays are special because sometimes you want to append elements, sometimes prepend and sometimes you want to merge them.

Mongodb handles this nicely (IMHO). It has a $push property (among others) that let you append elements to an array when updating a document.

Inspired on that this library has the following merging methods (note that to be merged, the arrays can have any depth as long as they have the same path):

Merge elements

This is the default behavior. It merges the arrays elements one by one. It will add elements to the end if there more on the right than on the left element.

const left = {
  foo: [1, 2, 3],
  bar: []
};

const right = {
  foo: [10, 20],
  bar: [10, 20, 30]
};

const result = merge(left, right) 

// Result
{
  foo: [10, 20, 3],
  bar: [10, 20, 30]
}

#push / #append

You can use the special property $push or $append to add elements to the end of the "left" array.

const left = [0, 1, 2];
const right = { $push: [3, 4, 5] };
const result = merge(left, right);

// Result
[0, 1, 2, 3, 4, 5]

#prepend

Similarly, you can use the property $prepend to add elements to the beginning of the "left" array.

const left = [0, 1, 2];
const right = { $prepend: [-2, -1] };
const result = merge(left, right);

// Result
[-2, -1, 0, 1, 2]

#set

Use #set when you want to completely replace "left" array by the "right" one.

const left = [0, 1, 2, 3, 4, 5, 6];
const right = { $set: [10, 20] };
const result = merge(left, right);

// Result
[10, 20]

$replace

Use $replace to replace or add indexed elements by their indexes. Indexes can be numbers or strings and cannot be less than 0 or NaN values.

With valid indexes:

const left = [10, 20, 30];
const right = { $replace: { 0: 100, '2': 300, 4: 400 } };
const result = merge(left, right);

// Result (note that the element with index 3 was never given)
[100, 20, 300, , 400]

With invalid indexes:

const left = [10, 20, 30];
const right = { $replace: { null: 0, 'foo': 0, true: 0, '-1': 0 } };
const result = merge(left, right);

// throws an Error

$insert

Use $insert to insert indexed elements at their indexes. Indexes can be numbers or strings and cannot NaN values. Notice that elements change places as you insert them. Negative numbers insert them to the end of the array. See Array.splice.

With positive indexes:

const left = [10, 20, 30];
const right = { $insert: { 0: 100, 2: 200, 10: 400 } };
const result = merge(left, right);

// Result (notice that the elements moved and the 400 was added to the last index)
[ 100, 10, 200, 20, 30, 400 ]

With negative indexes:

const left = [10, 20, 30];
const right = { $insert: { '-1': 100, '-2': 200, '-10': 0 } };
const result = merge(left, right);

// Result
[ 0, 10, 20, 200, 100, 30 ]

With invalid indexes:

const left = [10, 20, 30];
const right = { $insert: { null: 100, 'foo': 300, true: 400 } };
const result = merge(left, right);

// throws an Error

Skipping elements

If you skip some elements in the "right" array, the respective "left" elements will be kept in the result. This is not very useful for json merging since it's ot possible to create a sparse array per se, but it's a nice consequence of the merge method.

const left = [1, 20, 3, 40, 5, 60];
const right = [10, , 30, , 50];
const result = merge(left, right);

// Result
[10, 20, 30, 40, 50, 60]

Options

For now, no options yet.

Contributing

If you are nice enough you can submit bugs and features to the issue board and make this lib great and useful for you and the community.

But if you are really nice you can submit a PR and make this lib awesome!