Data get updated twice on button onClick event

Question

I've a very simple React Web App where I want to add new object of review to an array of an object:-

I'm using useReducer to handle default state of my data as show below:-

reducer function:-

const reducer = (state, action) => {
  switch (action.type) {
    case "ADD_REVIEW_ITEM":
      state.forEach(
        (data) =>
          data.id === action.payload.selectedDataId &&
          data.listOfReview.push(action.payload.newReview)
      );

      return [...state];
    default:
      return state;
  }
};

default data for my reducer:-

const data = [
  {
    id: 1607089645363,
    name: "john",
    noOfReview: 1,
    listOfReview: [
      {
        reviewId: 1607089645361,
        name: "john doe",
        occupation: "hero",
        rating: 5,
        review: "lorem ipsum"
      }
    ]
  },
  {
    id: 1507089645363,
    name: "smith",
    noOfReview: 1,
    listOfReview: [
      {
        reviewId: 1507089645361,
        name: "smith doe",
        occupation: "villain",
        rating: 5,
        review: "lorem ipsum"
      }
    ]
  }
];

App.js, demo of what's happening:-

import React, { useState, useEffect, useReducer } from "react";
import "./styles.css";

export default function App() {
  const [state, dispatch] = useReducer(reducer, data);

  // hnadle adding of new review
  const handleAddNewReview = (id) => {
    dispatch({
      type: "ADD_REVIEW_ITEM",
      payload: {
        selectedDataId: id,
        newReview: {
          reviewId: new Date().getTime().toString(),
          name: "doe doe",
          occupation: "doctor",
          rating: 5,
          review: "lorem ipsum"
        }
      }
    });
  };

  return (
    <>
      <div className="App">
        <h1>Hello CodeSandbox</h1>
        <h2>Start editing to see some magic happen!</h2>
      </div>
      {state?.length > 0 &&
        state.map((data) => (
          <div key={data.id}>
            <h1>{data.name}</h1>
            {data.listOfReview?.length > 0 &&
              data.listOfReview.map((review) => (
                <div key={review.reviewId}>
                  <h3>{review.name}</h3>
                  <p>{review.occupation}</p>
                </div>
              ))}
            <button onClick={() => handleAddNewReview(data.id)}>
              Add new review
            </button>
          </div>
        ))}
    </>
  );
}

The problem is, once I clicked the button for the first time, the state gets updated right. But if I click it for the second time, it somehow added TWO more of the same review. How should I change my code in reducer to fixed this issue?

This is a working sandbox of said case.

score 2 · Accepted Answer · answered Dec 07 '20 at 06:17

Try changing your reducer to be:

case "ADD_REVIEW_ITEM":
      return state.map((data) => {
        if (data.id === action.payload.selectedDataId) {
          return {
            ...data,
            listOfReview: [...data.listOfReview, action.payload.newReview]
          };
        }
        return data;
      });

Currently, you are mutating the state variable and pushing in an array which can lead to side-effect.

Data get updated twice on button onClick event

1 Answers1