Compare two objects (deep)

main.js

// main.js
import objectDifference from './utils/objectDifference'

const obj1 = {
  user: {
    info: {
      username: 'foo'
    }
  }
}

const obj2 = {
  user: {
    info: {
      username: 'bar'
    }
  }
}

const objDiff = objectDifference(obj1, obj2)

/*
objDiff === {
  user: {
    info: {
      username: 'bar'
    }
  }
}
*/

objectDifference.js

// objectDifference.js
export default (obj1, obj2) => {
  const compareObjLevel = (obj1, obj2, newObj) => {
    // Compare current level
    let newObjChanged = false
    for (const key in obj2) {
      // Check if obj1 is different with key
      if (!obj1.hasOwnProperty(key)) {
        // If different, add to new object
        newObj[key] = obj2[key]
        newObjChanged = true
        continue
      }

      if (typeof obj1[key] !== typeof obj2[key]) {
        // Different... add to new obj
        newObj[key] = obj2[key]
        newObjChanged = true
        continue
      }

      if (typeof obj1[key] === 'object') {
        newObj[key] = {}
        const newObjVal = compareObjLevel(obj1[key], obj2[key], newObj[key])
        if (newObjVal != null) {
          newObj[key] = newObjVal
          newObjChanged = true
        } else {
          delete newObj[key]
        }
        continue
      }

      if (obj1[key] !== obj2[key]) {
        newObj[key] = obj2[key]
        newObjChanged = true
        continue
      }
    }

    // Return different objects in obj2
    return newObjChanged ? newObj : null
  }

  return compareObjLevel(obj1, obj2, {}) || {}
}