js-struct-compare

Javascript library to compare two (JSON-serializable) structures and return their differences.

Installation

This library can be installed from the NPM package registry. Using NPM:

npm install --save js-struct-compare

Or using Yarn:

yarn add js-struct-compare

Usage

This package is meant to be consumed as an ES module. Its default export is a comparison function that takes a left and a right instance and returns an array of differences between them. These can be seen as the operations needed to transform left into right. An example:

import compare from "js-struct-compare";

const left = {
    "foo": {
        "bar": [ 42, 0 ],
    },
    "qux": "quux",
    "corge": "grault",
    "garply": [],
};
const right = {
    "foo": {
        "bar": [ 43, 0 ],
        "baz": 99,
    },
    "corge": "grault",
    "garply": {},
};

const differences = compare(left, right);
// => [
//   Difference{path: ['foo', 'bar', 0], type: 'changed', left_value: 42, right_value: 43},
//   Difference{path: ['foo', 'baz'], type: 'added', left_value: undefined, right_value: 99},
//   Difference{path: ['qux'], type: 'deleted', left_value: 'quux', right_value: undefined}
//   Difference{path: ['garply'], type: 'changed', left_value: [], right_value: {}},
// ]

Each Difference object contains:

• A path: an array of path elements traversed to the location of the differences. The path elements are strings in case of object properties and numbers in case of array keys.
• A type: describes the kind of difference. Can be one of the following:
  • Difference.TYPE_CHANGED = 'changed': both the left and the right instance have a value at the given path, but these values are different.
  • Difference.TYPE_ADDED = 'added': the left instance does not have a value at the given path, but the right instance does, i.e. the value was added in the transition from left to right.
  • Difference.TYPE_DELETED = 'deleted': the left instance has a value at the given path, but the right instance does not, i.e. the value was deleted in the transition from left to right.
• A left_value: the value the left instance has at the given path. Is undefined in case of an addition. Can be a non-scalar value, i.e. a struct in itself.
• A right_value: the value the right instance has at the given path. Is undefined in case of a deletion. Can be a non-scalar value, i.e. a struct in itself.

The Difference and Comparator classes can be accessed separately as named exports:

import { Difference, Comparator } from "js-struct-compare";

Versioning

This project adheres to Semantic Versioning.

Contributing

Contributions to this project are more than welcome.

License

This project is released under the MIT license.

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