Compare two JSON objects and just return another JSON object with only the changes

Compare Two JSON Objects and Return a New JSON Object with Only Changes

Introduction:

In the domain of programming, comparing JSON objects to identify differences and changes is a common task. By implementing a structured approach, we can efficiently compute and present the variations between two JSON objects in a new JSON object.

Implementation:

1. Initialize Variables:
   • Create two JSON objects, obj1 and obj2, to represent the original and modified JSON data, respectively.
   • Initialize an empty JSON object, obj3, to store the differences between the two objects.


2. Traverse Object Keys:
   • Utilize a for loop to iterate through the keys of obj1.
   • For each key, check whether obj2 possesses the same key.


3. Comparison and Storage:
   • If obj2 does not have the current key, it signifies a difference. Store the key and its value from obj1 in obj3.
   • If the values associated with the key in obj1 and obj2 are different, update the value in obj3 with the value from obj2.


4. Handle Nested Objects:
   • If the values associated with the key are objects, recursively call the comparison function on these nested objects.
   • This ensures that changes within nested objects are also captured and stored in obj3.


5. Return Result:
   • After processing all keys in obj1, obj3 will contain the differences between the two JSON objects.
   • Return obj3 as the final result.

Code Example:

function compareJSON(obj1, obj2) {
  var obj3 = {};
  for (var key in obj1) {
    if (!obj2.hasOwnProperty(key)) {
      obj3[key] = obj1[key];
    } else if (typeof obj1[key] === "object" && typeof obj2[key] === "object") {
      obj3[key] = compareJSON(obj1[key], obj2[key]);
    } else if (obj1[key] !== obj2[key]) {
      obj3[key] = obj2[key];
    }
  }
  return obj3;
}

var obj1 = {
  "name": "John Doe",
  "age": 30,
  "address": {
    "street": "123 Main Street",
    "city": "Anytown",
    "state": "CA"
  }
};

var obj2 = {
  "name": "Jane Smith",
  "age": 35,
  "address": {
    "street": "456 Elm Street",
    "city": "Anytown",
    "state": "CA"
  }
};

var obj3 = compareJSON(obj1, obj2);
console.log(obj3);

Output:

{
  "name": "Jane Smith",
  "age": 35,
  "address": {
    "street": "456 Elm Street"
  }
}

In this example, we have two JSON objects, obj1 and obj2, with some differences in values and a nested object. The compareJSON function successfully identifies these changes and returns a new JSON object, obj3, containing only the variations. By employing this approach, you can compare two JSON objects and obtain a concise representation of their differences in a new JSON object. This technique proves useful in various scenarios requiring data comparison and change tracking.