json-diff-ts
is a TypeScript library that calculates and applies differences between JSON objects. A standout feature is its ability to identify elements in arrays using keys instead of indices, which offers a more intuitive way to handle arrays. It also supports JSONPath, a query language for JSON, which enables you to target specific parts of a JSON document with precision.
Another significant feature of this library is its ability to transform changesets into atomic changes. This means that each change in the data can be isolated and applied independently, providing a granular level of control over the data manipulation process.
This library is particularly valuable for applications where tracking changes in JSON data is crucial. It simplifies the process of comparing JSON objects and applying changes. The support for key-based array identification can be especially useful in complex JSON structures where tracking by index is not efficient or intuitive. JSONPath support further enhances its capabilities by allowing precise targeting of specific parts in a JSON document, making it a versatile tool for handling JSON data.
Starting with version 3, json-diff-ts
now supports both ECMAScript Modules and CommonJS. This makes the library more versatile and compatible with various JavaScript environments. Whether you're working in a modern project that uses ES modules, or a Node.js project that uses CommonJS, you can now use json-diff-ts
seamlessly.
npm install json-diff-ts
In TypeScript or ES Modules, you can import the diff
function like this:
import { diff } from 'json-diff-ts';
In CommonJS, you can import the diff function like this:
const { diff } = require('json-diff-ts');
diff
Generates a difference set for JSON objects. When comparing arrays, if a specific key is provided, differences are determined by matching elements via this key rather than array indices.
import { diff } from 'json-diff-ts';
const oldData = {
planet: 'Tatooine',
faction: 'Jedi',
characters: [
{ id: 'LUK', name: 'Luke Skywalker', force: true },
{ id: 'LEI', name: 'Leia Organa', force: true }
],
weapons: ['Lightsaber', 'Blaster']
};
const newData = {
planet: 'Alderaan',
faction: 'Rebel Alliance',
characters: [
{ id: 'LUK', name: 'Luke Skywalker', force: true, rank: 'Commander' },
{ id: 'HAN', name: 'Han Solo', force: false }
],
weapons: ['Lightsaber', 'Blaster', 'Bowcaster']
};
const diffs = diff(oldData, newData, { characters: 'id' });
const expectedDiffs = [
{
type: 'UPDATE',
key: 'planet',
value: 'Alderaan',
oldValue: 'Tatooine'
},
{
type: 'UPDATE',
key: 'faction',
value: 'Rebel Alliance',
oldValue: 'Jedi'
},
{
type: 'UPDATE',
key: 'characters',
embeddedKey: 'id',
changes: [
{
type: 'UPDATE',
key: 'LUK',
changes: [
{
type: 'ADD',
key: 'rank',
value: 'Commander'
}
]
},
{
type: 'ADD',
key: 'HAN',
value: {
id: 'HAN',
name: 'Han Solo',
force: false
}
},
{
type: 'REMOVE',
key: 'LEI',
value: {
id: 'LEI',
name: 'Leia Organa',
force: true
}
}
]
},
{
type: 'UPDATE',
key: 'weapons',
embeddedKey: '$index',
changes: [
{
type: 'ADD',
key: '2',
value: 'Bowcaster'
}
]
}
];
Paths can be utilized to identify keys within nested arrays.
const diffs = diff(oldData, newData, { embeddedObjKeys { 'characters.subarray': 'id' }});
You can also designate the root by using '.' instead of an empty string ('').
const diffs = diff(oldData, newData, { embeddedObjKeys: { '.characters.subarray': 'id' } });
Determine if type changes are treated as a replace (remove, add) or as an update; default is replace.
const diffs = diff(oldData, newData, { treatTypeChangeAsReplace: false });
You can use a function to dynamically resolve the key of the object. The first parameter is the object and the second is to signal if the function should return the key name instead of the value. This is needed to flatten the changeset
const diffs = diff(oldData, newData, {
embeddedObjKeys: {
characters: (obj, shouldReturnKeyName) => (shouldReturnKeyName ? 'id' : obj.id)
}
});
If you're using the Map type, you can employ regular expressions for path identification.
const embeddedObjKeys: EmbeddedObjKeysMapType = new Map();
embeddedObjKeys.set(/^char\w+$/, 'id'); // instead of 'id' you can specify a function
const diffs = diff(oldObj, newObj, { embeddedObjKeys });
Compare string arrays by value instead of index
const diffs = diff(oldObj, newObj, { embeddedObjKeys: { stringArr: '$value' } });
atomizeChangeset
Transforms a complex changeset into a list of atomic changes, each describable by a JSONPath.
const atomicChanges = atomizeChangeset(diffs);
// Restore the changeset from a selection of atomic changes
const changeset = unatomizeChangeset(flatChanges.slice(0, 3));
// Alternatively, apply the changes using a JSONPath-capable library
// ...
Atomic Changes will have the following structure:
[
{ type: 'UPDATE', key: 'planet', value: 'Alderaan', oldValue: 'Tatooine', path: '$.planet', valueType: 'String' },
// ... Additional flat changes here
{ type: 'ADD', key: 'rank', value: 'Commander', path: "$.characters[?(@.id=='LUK')].rank", valueType: 'String' }
];
applyChange
const oldData = {
// ... Initial data here
};
// Sample diffs array, similar to the one generated in the diff example
const diffs = [
// ... Diff objects here
];
changesets.applyChanges(oldData, diffs);
expect(oldData).to.eql({
// ... Updated data here
});
revertChange
const newData = {
// ... Updated data here
};
// Sample diffs array
const diffs = [
// ... Diff objects here
];
changesets.revertChanges(newData, diffs);
expect(newData).to.eql({
// ... Original data restored here
});
jsonPath
The json-diff-ts
library uses JSONPath to address specific parts of a JSON document in both the changeset and the application/reversion of changes.
const jsonPath = changesets.jsonPath;
cost data = {
// ... Some JSON data
};
const value = jsonPath.query(data, '$.characters[?(@.id=="LUK")].name');
expect(value).to.eql(['Luke Skywalker']);
Contributions are welcome! Please follow the provided issue templates and code of conduct.
Reach out to the maintainer via LinkedIn or Twitter:
Discover more about the company behind this project: hololux
This project takes inspiration and code from diff-json by viruschidai@gmail.com.
json-diff-ts is open-sourced software licensed under the MIT license.
The original diff-json project is also under the MIT License. For more information, refer to its license details.