flatten-immutable-list.js

// must run in a context where Immutable is available, like in the console here: https://facebook.github.io/immutable-js/docs/#/

const flattenList = items => {
  return items.reduce((result, item) => {
    result = result.push(item)
    return item.has('children') ? result.concat(flattenList(item.get('children'))) : result
  }, Immutable.List())
}

const nestedList = [
  {
    value: '1',
    children: [
      { value: '1.1' },
      { value: '1.2' }
    ]
  }, {
    value: '2',
    children: [
      { value: '2.1' }
    ]
  }, {
    value: '3',
    children: [
      { value: '3.1',
        children: [
          {
            value: '3.1.1'
          }, {
            value: '3.1.2'
          }
        ]
      }
    ]
  }
]

const nestedImmutableList = Immutable.fromJS(nestedList)

const flattenedImmutableList = flattenList(nestedImmutableList)

const expectedResult = ["1", "1.1", "1.2", "2", "2.1", "3", "3.1", "3.1.1", "3.1.2"]

flattenedImmutableList.map( list => list.get('value') ).equals(Immutable.fromJS(expectedResult)) // true