Property id does not exist on type 'never'

Question

I'm trying to do a .map function into a state array in Redux with Typescript, the problem is that it's throwing an error

[ts] Property 'id' does not exist on type 'never'

in the landing.id if statement, since its an array of objects the code makes sense for me but seems that I'm missing something there

export default function landingReducer (state = [], action) {
switch(action.type) {
  case ActionTypes.ADD_LANDING:
    return [...state, action.landing]
  case ActionTypes.EDIT_LANDING:
    return state.map(landing => {
      if (action.landing.id == landing.id) {
        return landing;
      }
    })

Thanks in advance!

Answer 1

It's probably due to types missing for the state and/or action arguments. Try this code that should work with TypeScript 2.4+, inspired by this article:

interface Landing {
    id: any;
}

enum ActionTypes {
    ADD_LANDING  = "ADD_LANDING",
    EDIT_LANDING = "EDIT_LANDING",
    OTHER_ACTION = "__any_other_action_type__"
}

interface AddLandingAction {
    type: ActionTypes.ADD_LANDING;
    landing: Landing;
}

interface EditLandingAction {
    type: ActionTypes.EDIT_LANDING;
    landing: Landing;
}

type LandingAction =
    | AddLandingAction
    | EditLandingAction;

function landingReducer(state: Landing[], action: LandingAction) {
    switch (action.type) {
        case ActionTypes.ADD_LANDING:
            return [...state, action.landing]

        case ActionTypes.EDIT_LANDING:
            return state.map(landing => {
                if (action.landing.id === landing.id) {
                    return landing;
                }
            });
    }
}