Get previous and current state in Redux's reducer

December 7, 2021

I start to study Redux.
In my app i have a button. I push in this btn and get an object.
This object income to reducer in action.payload.
Object change everytime, when i push in the button.
How i can save all previous state in reducer, and add the current state?
To make something like that:

 if (action.type === "ADD_ITEM") {
        return {
          items: [all previous state, + current state],
        };
      }

All code in reducer

const initialState = {
  items: [],
};

const basket = (state = initialState, action) => {
  if (action.type === "ADD_ITEM") {
    return {
      items: [action.data],
    };
  }
  return state;
};

export default basket;

>Solution :

If you want to append new data into an array you can shallow copy the existing state array and append the new data to the end.

const initialState = {
  items: [],
};

const basket = (state = initialState, action) => {
  if (action.type === "ADD_ITEM") {
    return {
      ...state,         // shallow copy existing state
      items: [
        ...state.items, // shallow copy existing items
        action.data,    // append new data
      ],
    };
  }
  return state;
};