Append Previous State to New State in Redux-CodePudding

I have this app which uses the first createAsyncThunk to get the first page from the API, then I want the second createAsyncThunk, which gets the next page, to fire when the user reaches the bottom of the page and get the data in the infinite scrolling method.

// Gets the First 10 Posts from the API
export const getPosts = createAsyncThunk(
  "post/getPosts",
  async (apiAddress) => {
    const response = await fetch(apiAddress);
    if (!response.ok) throw new Error("Request Failed!");
    const data = await response.json();
    return data;
  }
);

// Loads the Next 10 Posts
export const getMorePosts = createAsyncThunk(
  "post/getMorePosts",
  async (apiAddress) => {
    const response = await fetch(apiAddress);
    if (!response.ok) throw new Error("Request Failed!");
    const data = await response.json();
    return data;
  }
);

const redditPostSlice = createSlice({
  name: "post",
  initialState: {
    redditPost: {},
    isLoading: false,
    hasError: false,
    moreIsLoading: false,
    moreHasError: false,
  },
  extraReducers: (builder) => {
    builder
      .addCase(getPosts.pending, (state) => {
        state.isLoading = true;
        state.hasError = false;
      })
      .addCase(getPosts.fulfilled, (state, action) => {
        state.redditPost = action.payload.data;
        state.isLoading = false;
        state.hasError = false;
      })
      .addCase(getPosts.rejected, (state) => {
        state.isLoading = false;
        state.hasError = true;
      })
      .addCase(getMorePosts.pending, (state) => {
        state.moreIsLoading = true;
        state.moreHasError = false;
      })
      .addCase(getMorePosts.fulfilled, (state, action) => {
        state.redditPost = action.payload.data;
        state.moreIsLoading = false;
        state.moreHasError = false;
      })
      .addCase(getMorePosts.rejected, (state) => {
        state.moreIsLoading = false;
        state.moreHasError = true;
      });
  },
});

My problem is that the state of the app changes to the second page and the first page contents are gone.

I know my problem is here state.redditPost = action.payload.data but I don't know how I can append this new state to the previous one.

I've been at this for hours and don't really know what to do anymore.

Is there any way to append the new state to the previous state?

CodePudding user response：

I would assume that the payload data has an array of children. Like this example of response found online:

{
   kind: "Listing",
   data: {
      ...
      children: [
          {kind: "t3", data: {...}}
          {kind: "t3", data: {...}}
          {kind: "t3", data: {...}}
          ...
      ]
      ...
   }
}

So you would need to make redditPost be an array. Also semantically is should be redditPosts to denote array.

  initialState: {
    redditPost: {},
    ...

and then when you're updating it one of the easiest ways is using ES6 spread

state.redditPost = {
    ...state.redditPost,
    after: action.payload.data.after,
    children: [
        ...state.redditPost.children,
        ...action.payload.data.children
    ]
}