无法读取未定义的属性（读取 'defaultSize'）

Question

我正在尝试在我的 MERN 项目中使用 useState，并且我在 MongoDB 中定义了 defaultSize，并且正在尝试通过 product.defaultSize 来使用 State。如果我更改我的一些代码（例如添加 console.log("hello")）并保存它，错误就会消失并正常加载。但是如果我刷新页面，错误又回来了？

import { useEffect, useState } from "react";

import { getProductDetails } from "../redux/actions/productActions";

import { SizeOptions } from '../components/SizeOptions';

const ProductScreen = ({match}) => {

    const dispatch = useDispatch();

    const productDetails = useSelector(state => state.getProductDetails);
    const { loading, error, product } = productDetails;

    const [ src, setSrc ] = useState(product.defaultSize);


    useEffect(() => {
    if (product && match.params.id !== product._id) {
        dispatch(getProductDetails(match.params.id));
        }
    }, [dispatch, match, product]);
    
    <div className='sizebuttons'>
        {product && (product.size || []).map((size, index) => (<SizeOptions  key={index} size={size} changeSrc={src => setSrc(src)}/>))}
    </div>
    
return (
    <model-viewer
        id="model-viewer"
        src={src}
        alt={product.productName}
        ar
        ar-modes="scene-viewer quick-look"
        ar-placement="floor"
        shadow-intensity="1"
        camera-controls
        min-camera-orbit={product.mincameraorbit} 
        max-camera-orbit={product.maxcameraorbit}
        interaction-prompt="none">  
            <button slot="ar-button" className="ar-button">
                View in your space
            </button>
    </model-viewer>
)};

我也尝试过将其更改为 useState(product?.defaultSize);，因为我在这里看到另一个 post 说可以，但我没有成功。如您所知，所有其他 product.otherstuff 工作正常。任何帮助将不胜感激！

Answer 1

import { useEffect, useState } from "react";

import { getProductDetails } from "../redux/actions/productActions";

import { SizeOptions } from '../components/SizeOptions';

const ProductScreen = ({match}) => {

    const dispatch = useDispatch();

    const productDetails = useSelector(state => state.getProductDetails);
    const { loading, error, product } = productDetails;

    const [ src, setSrc ] = useState();


    useEffect(() => {
    if (product && match.params.id !== product._id) {
        dispatch(getProductDetails(match.params.id));
        }
    }, [dispatch, match, product]);
    
    <div className='sizebuttons'>
        {product && (product.size || []).map((size, index) => (<SizeOptions  key={index} size={size} changeSrc={src => setSrc(src)}/>))}
    </div>
    
return (
    <model-viewer
        id="model-viewer"
        src={src || product.defaultSize}
        alt={product.productName}
        ar
        ar-modes="scene-viewer quick-look"
        ar-placement="floor"
        shadow-intensity="1"
        camera-controls
        min-camera-orbit={product.mincameraorbit} 
        max-camera-orbit={product.maxcameraorbit}
        interaction-prompt="none">  
            <button slot="ar-button" className="ar-button">
                View in your space
            </button>
    </model-viewer>
)};

无法读取未定义的属性（读取 'defaultSize'）

Cannot read properties of undefined (reading 'defaultSize')

javascript

reactjs

mern