Array.push() function 在 React JS 中不起作用

Question

I have an object which represents a recipe, whenever I click the "Add" button my function is supposed to add that corresponding recipe to an empty object array, but oddly only on recipe object gets added to the empty array and when i try to add more than one then it throw this at me: favList.push is not a function.

My HTML Code:

---

import React from 'react'
import './home.css'

const Home = (props) => {
return <div className="home">
               
                     <div className="wrapper">
                            {props.items.map((item) => {
                                  return  <div className="flexIt">
                                                    {item.ingredients.map((ingredient) => 
                                                        <ol>
                                                            <li>{ingredient}</li>
                                                        </ol>
                                                    )}        
                                                </div>
                                            </div>
                                            <div className="closeBtn">
                                                <button onClick = {() => {props.onRemove(item)}} >X</button>
                                                <button onClick = {() => {props.addItemToFav(item)}} >Add</button>
                                            </div>
                                          </div>})}
                            </div>
                     </div> 
                </div>
            </div>
}

export default Home

---

My JavaScriipt code:

---

import './App.css';
import Home from './components/Home';
import AddRecipe from './components/AddRecipe';
import { useNavigate } from 'react-router'
import items from './data';
import React, { useState } from 'react';
import {Routes, Route} from 'react-router-dom';

    const App = () => {
    const navigate = useNavigate(); 
    const [favList, setFavList] = useState([]);
    
  const addToFav = (itemToBeAdded) => {
      setFavList(favList.push([itemToBeAdded]));
      console.log(favList);   
  }
  return (

      <Routes>
        <Route exact path="/" element={<Home onRemove={removeItem} addItemToFav={addToFav} items={itemsList}/>} />
        <Route path="/addRecipe" element={<AddRecipe onAddRecipe={(newRecipe) => {
        addRecipe(newRecipe);
        navigate('/');
      }}
    />} />
        </Routes>
  );
}

export default App;

***

Answer 1

First, push will mutate the existing array.

Then you pass the return value to setFavList (which is a number representing the length of the array).

You need to pass a new array to setFavList . You can't (usefully) pass that number or the original (but mutated) array (since it would detect it is the same array and do nothing).

For example:

const addToFav = (itemToBeAdded) => {
  const replacementList = [...favList, itemToBeAdded];
  setFavList(replacementList);
}

(Note also that itemToBeAdded probably shouldn't be wrapped in an extra array.)

Then your attempt to log the new value needs to be moved because addToFav will have closed over the original value. This is explained by answers to this question