something.jsx

const something = (state) => {
  let newState = { ...state }
  const indexPanda = newState.items.indexOf('panda')
  if (indexPanda !== -1) {
    newState.items.splice(indexPanda, 1)
  }
  return newState
}

const initialState = {
  items: [],
}

const reducer = (state, action) => {
  switch (action.type) {
    case 'add-item':
      return { ...state, items: [...something(state).items, action.item] }
    case 'clear':
      return { ...initialState }
    default:
      return state
  }
}