I have two JavaScript objects (of arbitrary depth) that have much of the same information.

I'm looking for help getting the shared data between two objects.

For example:

const a = {
  name: 'Alice',
  features: {
    speed: 3,
    strength: 90,
    mind: {
      power: 42
    }
  }
};

const b = {
  name: 'Bob',
  features: {
    speed: 3,
    stamina: 1,
    mind: {
      power: 42,
      flexibility: 0,
      telekinesis: 42
    }
  }
};

My goal is to e up with a solution to produce the data that they share:

const shared = {
  features: {
    speed: 3,
    mind: {
      power: 42
    }
  }
}

The real data I'm operating on is nested arbitrarily deep (often dozens of objects within objects), but I'm hoping the above examples are helpful.

This is a one-off task so I'm not particularly concerned with performance, and I'm happy to use any library as long as it works. Thanks for the help!

I have two JavaScript objects (of arbitrary depth) that have much of the same information.

I'm looking for help getting the shared data between two objects.

For example:

const a = {
  name: 'Alice',
  features: {
    speed: 3,
    strength: 90,
    mind: {
      power: 42
    }
  }
};

const b = {
  name: 'Bob',
  features: {
    speed: 3,
    stamina: 1,
    mind: {
      power: 42,
      flexibility: 0,
      telekinesis: 42
    }
  }
};

My goal is to e up with a solution to produce the data that they share:

const shared = {
  features: {
    speed: 3,
    mind: {
      power: 42
    }
  }
}

The real data I'm operating on is nested arbitrarily deep (often dozens of objects within objects), but I'm hoping the above examples are helpful.

This is a one-off task so I'm not particularly concerned with performance, and I'm happy to use any library as long as it works. Thanks for the help!

• javascript
• object
• nested
• javascript-objects

3 Answers 3

You could use an recursve approach by checking the existence of properties in both objects, truthy properties and same object type or same values.

The use of a variable temp prevents empty nested objects.

function mon(object1, object2) {
    return Object.assign(...Object.keys(object1).map(k => {
        var temp;
        if (!(k in object2)) {
            return {};
        }
        if (object1[k] && typeof object1[k] === 'object' &&
            object2[k] && typeof object2[k] === 'object') {
            temp = mon(object1[k], object2[k]);
            return Object.keys(temp).length ? { [k]: temp } : {};
        }
        if (object1[k] === object2[k]) {
           return { [k]: object1[k] };
        }
        return {};
    }));
}

const
    a = { name: 'Alice', features: { speed: 3, strength: 90, mind: { power: 42 } } };
    b = { name: 'Bob', features: { speed: 3, stamina: 1, mind: { power: 42, flexibility: 0, telekinesis: 42 } } };

console.log(mon(a, b));

.as-console-wrapper { max-height: 100% !important; top: 0; }

You can use the for...in iteration to loop through the object and check it's properties. Please, see in the below code if is that what you want.

const a = {
  name: 'Alice',
  features: {
    speed: 3,
    strength: 90,
    mind: {
      power: 42
    }
  }
};

const b = {
  name: 'Bob',
  features: {
    speed: 3,
    stamina: 1,
    mind: {
      power: 42,
      flexibility: 0,
      telekinesis: 42
    }
  }
};

function equalProps(a,b){
  var newObj = {}; 
  for (var key in a){
    if (typeof a[key] === 'object'){
      var obj = equalProps(a[key], b[key]);
      newObj[key] = obj;
    }else if (a[key] == b[key]){
      newObj[key] = a[key];
    }
  }
  return newObj;
}

console.log(equalProps(a,b))

It looks like the other answers in this thread crashed when an object value was undefined, so I bined the best parts of each answer to e up with a robust solution:

const isObj = x => typeof x === 'object'

const mon = (a, b) => {
  let result = {}

  if (([a, b]).every(isObj)) {
    Object.keys(a).forEach((key) => {
      const value = a[key]
      const other = b[key]

      if (isObj(value)) {
        result[key] = mon(value, other)
      } else if (value === other) {
        result[key] = value
      }
    })
  }

  return result
}