JS Object Deep Flatten (ES6)

flatten.js

/**
 * Flattens a nested object into a flat form delimited by "." character at
 * each level. Check tests for an example.
 *
 * @param {Object} nestedObject
 * @returns {Object}
 */
export const flattenObject = nestedObject => {
  const flattenedObject = {}
  const keys = Object.keys(nestedObject)

  for (let i = 0; i < keys.length; i += 1) {
    const key = keys[i]
    const value = nestedObject[key]

    if (value && typeof value === 'object') {
      const innerValues = flattenObject(value)
      const innerKeys = Object.keys(innerValues)
      for (let j = 0; j < innerKeys.length; j += 1) {
        const innerKey = innerKeys[j]

        flattenedObject[`${key}.${innerKey}`] = innerValues[innerKey]
      }
    } else {
      flattenedObject[key] = nestedObject[key]
    }
  }

  return flattenedObject
}

flatten.test.js

// JEST

describe('flattenObject()', () => {
  it('should correctly flatten the object', () => {
    const originalObject = {
      key1: {
        key2: {
          key3: 'val3',
          key4: 'val4'
        },
        key5: 'val5'
      },
      key6: {
        key7: 'val7'
      },
      key8: 'val8'
    }

    const expectedObject = {
      'key1.key2.key3': 'val3',
      'key1.key2.key4': 'val4',
      'key1.key5': 'val5',
      'key6.key7': 'val7',
      key8: 'val8'
    }

    expect(flattenObject(originalObject)).toEqual(expectedObject)
  })
})