Recursive merging of objects in javascript

Question

I'm currently working on a project with react and I'm facing a problem in merging two objects when using setState method. I have two objects similar to

person1 = {
    name: 'ramya',
    age: 21,
    gender: 'f',
    skills:{
        technicalSkills: {
            languages: ['C', 'C++', 'Java'],
            operatingSystems: ['Unix', 'Linux']
        },
        linguisticSkills: {
            toSpeak: ['English', 'Tamil'],
            toRead: ['English']
        }
    },
}

obj2 = {
    skills: {
        linguisticSkills: {
            toRead: ['English', 'Tamil']
        }
    }
}

I want to change state of person 1's skills.linguisticSkills to

linguisticSkills: {
                toSpeak: ['English', 'Tamil'],
                toRead: ['English', 'Tamil']
} 

skills.linguisticSkills.toSpeak and skills.linguisticSkills.toRead keep changing i.e items are added or removed. Whenever it is changes how do I merge person1 and obj2 in setState so I end up in the right state?

UPDATE: _.merge fails for a case like this:

person1 = {
        name: 'ramya',
        age: 21,
        gender: 'f',
        skills:{
            technicalSkills: {
                languages: ['C', 'C++', 'Java'],
                operatingSystems: ['Unix', 'Linux']
            },
            linguisticSkills: {
                toSpeak: ['English', 'Tamil'],
                toRead: ['English', 'Tamil', 'Telugu']
            }
        },
    }

    obj2 = {
        skills: {
            linguisticSkills: {
                toRead: ['English', 'Tamil']
            }
        }
    }

It gives the result same as person 1 whereas

{
        name: 'ramya',
        age: 21,
        gender: 'f',
        skills:{
            technicalSkills: {
                languages: ['C', 'C++', 'Java'],
                operatingSystems: ['Unix', 'Linux']
            },
            linguisticSkills: {
                toSpeak: ['English', 'Tamil'],
                toRead: ['English', 'Tamil']
            }
        },
    }

is expected.

Answer 1

Lodash's _.merge() is recursive. If you need more granular control about the merge process, you can use _.mergeWith().

const person1 = {"name":"ramya","age":21,"gender":"f","skills":{"technicalSkills":{"languages":["C","C++","Java"],"operatingSystems":["Unix","Linux"]},"linguisticSkills":{"toSpeak":["English","Tamil"],"toRead":['English', 'Tamil', 'Telugu']}}}

const obj2 = {"skills":{"linguisticSkills":{"toRead":["English","Tamil"]}}}

const result = _.mergeWith({}, person1, obj2, (objValue, srcValue) => {
  if( _.isArray(srcValue)) {
    return srcValue;
  }
});

console.log(result);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.4/lodash.min.js"></script>

Answer 2

check out https:How to deep merge instead of shallow merge?

/**
 * Simple object check.
 * @param item
 * @returns {boolean}
 */
export function isObject(item) {
  return (item && typeof item === 'object' && !Array.isArray(item));
}

/**
 * Deep merge two objects.
 * @param target
 * @param ...sources
 */
export function mergeDeep(target, ...sources) {
  if (!sources.length) return target;
  const source = sources.shift();

  if (isObject(target) && isObject(source)) {
    for (const key in source) {
      if (isObject(source[key])) {
        if (!target[key]) Object.assign(target, { [key]: {} });
        mergeDeep(target[key], source[key]);
      } else {
        Object.assign(target, { [key]: source[key] });
      }
    }
  }

  return mergeDeep(target, ...sources);
}

// Code copied from linked Stack Overflow question
// https://stackoverflow.com/questions/27936772/how-to-deep-merge-instead-of-shallow-merge
// Answer by Salakar:
// https://stackoverflow.com/users/2938161/salakar