When it comes to comparing and patching JSON objects, several libraries are available to developers. In this article, we'll explore three popular JSON diff libraries: fast-json-patch, jsondiffpatch, and jsonpatch. We'll compare their features, performance, and use cases to help you choose the right tool for your project.
Overview of Libraries
1. fast-json-patch
fast-json-patch is a lean and efficient JavaScript implementation of the JSON-Patch standard (RFC 6902). It provides functionality to apply patches on object trees for incoming traffic and generate patches for outgoing traffic.
Key features:
- Small footprint (0.5 KB minified and gzipped)
- Supports both applying and generating patches
- Uses ES6/7 Object.observe() when available
- Compatible with browsers and Node.js
2. jsondiffpatch
jsondiffpatch is a comprehensive library for diffing and patching JavaScript objects. It offers a range of features and formatters, making it versatile for various use cases.
Key features:
- Supports diffing, patching, and unpacking
- Multiple output formatters (HTML, console, annotated JSON)
- Smart array diffing using LCS (Longest Common Subsequence)
- Customizable object matching for arrays
- Reversible deltas
- JSON Patch format (RFC 6902) support
3. jsonpatch
jsonpatch is the reference implementation of the JSON Patch standard (RFC 6902). It provides a standardized way to describe changes to a JSON document.
Key features:
- Implements the JSON Patch standard
- Supports add, remove, replace, move, copy, and test operations
- Uses JSON Pointer for addressing parts of a JSON document
- Language-agnostic with implementations available in multiple programming languages
Performance Comparison
When it comes to performance, jsondiffpatch stands out as the fastest npm library among the three. This is one of the primary reasons why we use jsondiffpatch in the json-compare tool tool.
While specific benchmarks can vary depending on the use case and data structure, jsondiffpatch generally outperforms other libraries due to its optimized algorithms and efficient implementation. The library's smart array diffing using LCS contributes significantly to its performance, especially when dealing with large arrays of objects.
fast-json-patch, while lightweight and efficient, may not match jsondiffpatch's performance in complex scenarios, particularly when dealing with nested structures or large arrays. However, its small footprint makes it an excellent choice for projects where minimizing bundle size is crucial.
jsonpatch, being the reference implementation, focuses more on standard compliance than raw performance. While it provides a solid foundation, it may not be the best choice for high-performance applications dealing with large or complex JSON structures.
How jsondiffpatch Works Internally
To better understand why jsondiffpatch performs so well, let's delve into its internal workings:
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Object Comparison: jsondiffpatch uses a recursive approach to compare objects. It traverses the structure of both objects simultaneously, identifying additions, deletions, and modifications.
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Array Diffing: For arrays, jsondiffpatch employs the Longest Common Subsequence (LCS) algorithm. This allows it to efficiently detect moved items within an array, rather than treating them as deletions and additions.
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Customizable Object Matching: When diffing arrays of objects, jsondiffpatch allows you to specify an
objectHashfunction. This function determines how objects are matched across the two arrays, enabling more intelligent diffing. -
Delta Format: jsondiffpatch uses a compact delta format to represent changes. This format is designed to be both human-readable and efficient for machine processing.
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Plugins and Filters: The library uses a Pipes & Filters pattern for its core operations (diff, patch, reverse), making it highly customizable and extensible.
Interpreting jsondiffpatch Results
Understanding the delta format used by jsondiffpatch is crucial for interpreting its results. Here's a brief guide:
const left = { a: 1, b: { c: 2 } };
const right = { a: 1, b: { c: 3 }, d: 4 };
const delta = jsondiffpatch.diff(left, right);
console.log(delta);
This might produce a delta like:
{
b: { c: [2, 3] }, // Changed value
d: [4]
}
Interpreting the delta:
- For changed values, the array
[oldValue, newValue]is used. - For added properties, an array with a single element
[newValue]is used. - For deleted properties, an array with
[oldValue, 0, 0]is used. - For arrays, a special
_t: 'a'property indicates array operations.
When to Choose Each Library
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Choose jsondiffpatch when:
- Performance is a top priority
- You need flexible formatting options (HTML, console output)
- You're dealing with complex nested structures or large arrays
- You want to customize object matching in arrays
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Choose fast-json-patch when:
- You need a lightweight solution with a small footprint
- Strict adherence to the JSON Patch standard is required
- You're working in a browser environment and want to leverage Object.observe() when available
-
Choose jsonpatch when:
- You need a standardized, language-agnostic approach
- You're working on a project that requires strict compliance with RFC 6902
- You need implementations in multiple programming languages
Closing Thoughts
While all three libraries offer JSON diffing and patching capabilities, jsondiffpatch stands out for its performance and feature set. Its smart diffing algorithms, especially for arrays, make it the fastest option among npm libraries. This performance advantage, combined with its flexibility and extensive formatting options, makes it an excellent choice for most JavaScript projects dealing with JSON comparison and patching.
However, the choice of library should ultimately depend on your specific project requirements. If you need a lightweight solution or strict adherence to the JSON Patch standard, fast-json-patch or jsonpatch might be more suitable.
In json-compare tool, we've chosen jsondiffpatch due to its superior performance and rich feature set, allowing us to provide fast and accurate JSON comparisons for our users.