Json-object-merge NPM

json-object-merge

Merge JSON Objects using rules

More often we try to merge JSON objects into one. Even though this seems easy, many times it gets complicated. This library helps to recursively merge the JSON Objects based on rules. Rules give a hint on how to merge at each level of the JSON depth.

Usage

import JSONObjectMerge from "json-object-merge";

// in CommonJS environments
const JSONObjectMerge = require("json-object-merge");

// source is merged into target using rules and new object is returned
const merged = JSONObjectMerge(target, source, rules);

// when 4th parameter is true, returns the report containing the updatedPaths in the merged object
const mergedWithReport: {
  merged: unknown;
  report: {
    updatedPaths: {
      path: Path;
      operation: Operation;
      count?: number; // number of items appended/prepended for APPEND/PREPEND operations
    }[];
  };
} = JSONObjectMerge(target, source, rules, true);

JSONObjectMerge merges the source object recursively into the target object in the following manner.
If source is

Primitive type, the value is REPLACED with the value in the source.
Array, each item of the array is recursively COMBINED with the item from the source array
Object, each property is recursively COMBINED with the property from the source.

The default operation on Array and Object can be altered by specifying rules.

Merge Operations

Data Type	Operations	Default Operation
Primitive	REPLACE - The value is replaced	REPLACE
Array	REPLACE - The whole Array is relpaced COMBINE - The items are merged recursively APPEND - The source items are appended to the target PREPPEND - The source items are prepended to the target	COMBINE
Object	REPLACE - The whole Object is relpaced COMBINE - The properties are merged recursively	COMBINE

Rules Definition

The rules parameter is a JSON Path to the Operation map

For the sample JSON data mentioned at https://www.npmjs.com/package/jsonpath

const rules = {
  "$.store.book[*].author": "REPLACE", // replaces auther of all books inside the store
  "$..book": "APPEND", // append to books array
  "$..bicycle": "COMBINE" // Merge the properties of bicycle
};

Important considerations for rules

The JSON path is evaluated on the target object, not the source
If the type of value is not allowing the specified operation, then the default operation for the data type is used.

Examples

Merge without any custom rules

const target = {
  store: {
    book: [
      {
        category: "reference",
        author: "Nigel Rees",
        title: "Sayings of the Century",
        price: 8.95
      }
    ],
    bicycle: {
      color: "red",
      price: 19.95
    }
  }
};

const source = {
  store: {
    book: [
      {
        isbn: "0-044-40080-2",
        price: 9.05
      },
      {
        category: "fiction",
        author: "Evelyn Waugh",
        title: "Sword of Honour",
        isbn: "0-679-43136-5",
        price: 12.99
      }
    ]
  }
};
const merged = JSONObjectMerge(target, source);

expect(merged).toEqual({
  store: {
    // object is merged recursively
    book: [
      {
        // item at index 0 is merged
        category: "reference",
        author: "Nigel Rees",
        title: "Sayings of the Century",
        isbn: "0-044-40080-2", // isbn is added
        price: 9.05 // price is replaced
      },
      {
        // the new item is added
        category: "fiction",
        author: "Evelyn Waugh",
        title: "Sword of Honour",
        isbn: "0-679-43136-5",
        price: 12.99
      }
    ],
    bicycle: {
      color: "red",
      price: 19.95
    }
  }
});

Merge with rules

const target = {
  store: {
    book: [
      {
        category: "reference",
        author: "Nigel Rees",
        title: "Sayings of the Century",
        price: 8.95
      }
    ],
    bicycle: {
      color: "red",
      price: 19.95
    }
  }
};

const source = {
  store: {
    book: [
      {
        category: "fiction",
        author: "Evelyn Waugh",
        title: "Sword of Honour",
        isbn: "0-679-43136-5",
        price: 12.99
      }
    ]
  }
};
const merged = JSONObjectMerge(target, source, { "$.store.book": "PREPEND" });

expect(merged).toEqual({
  store: {
    book: [
      {
        // books from source are prepended to the original array
        category: "fiction",
        author: "Evelyn Waugh",
        title: "Sword of Honour",
        isbn: "0-679-43136-5",
        price: 12.99
      },
      {
        category: "reference",
        author: "Nigel Rees",
        title: "Sayings of the Century",
        price: 8.95
      }
    ],
    bicycle: {
      color: "red",
      price: 19.95
    }
  }
});

Merge with report

JSONObjectMerge returns the report containing paths in the merged object which are originally from the source

const target = {
  store: {
    bicycle: {
      color: "red"
    }
  }
};

const source = {
  store: {
    bicycle: {
      price: 19.95
    }
  }
};

const mergedWithReport = JSONObjectMerge(target, source, undefined, true);

expect(merged).toEqual({
  merged: {
    store: {
      bicycle: {
        color: "red",
        price: 19.95
      }
    }
  },
  report: {
    updatedPaths: [
      { path: ["$", "store", "bicycle", "price"], operation: "COMBINE" }
    ]
  }
});