TypeError: Cannot read property 'length' of null in React Project

user_14498654 0
Viewed 12368

The code seems to be fine but it's giving this error. It says TypeError: Cannot read property 'length' of null in React Project. I have posted the code below. I am using React Js to build this. Help, please.

import React, {useEffect} from 'react'
import { Link } from 'react-router-dom'
import { useDispatch, useSelector } from 'react-redux'
import { Row, Col, ListGroup, Image, Form, Button, Card } from 'react-bootstrap'
import Message from '../components/Message'
import { addToCart } from '../actions/cartActions'

function CartScreen({ match, location, history }) {
    const productId = match.params.id
    const qty = location.search ? Number(location.search.split('=')[1]) : 1
    
    const dispatch = useDispatch()

    const cart = useSelector(state => state.cart)
    const { cartItems } = cart

    useEffect(() => {
        if (productId){
            dispatch(addToCart(productId, qty))
        }
    }, [dispatch, productId, qty])


    return (
        <Row>
            <Col md={8}>
                <h1>Shopping Cart</h1>
                {cartItems.length === 0 ? (
                    <Message variant='info'>
                        Your cart is empty <Link to='/'>Go Back</Link>
                    </Message>
                ) : (
                        <ListGroup variant='flush'>
                            
                        </ListGroup>
                    )}
            </Col>
        </Row>
    )
}

export default CartScreen
typeerror reactjs javascript
3 Answers

Like the error say, it's just because your cartItems is null.

The variable can be null and defined 1 seconde after, but when the variable is null you have this error so you never see the variable with no null value.

Here is three way to fix your probleme.

1)

{cartItems?.length === 0 ? ( // add a ?. to check if variable is null
  <Message variant='info'>
    Your cart is empty <Link to='/'>Go Back</Link>
  </Message>
) : (
  <ListGroup variant='flush'>

  </ListGroup>
)}

{cartItems && cartItems.length === 0 ? ( // you check if the var is defined before check the length
  <Message variant='info'>
    Your cart is empty <Link to='/'>Go Back</Link>
  </Message>
) : (
  <ListGroup variant='flush'>

  </ListGroup>
)}

function CartScreen({ match, location, history }) {
    // ...

    // add a conditional render
    if (!cartItems) return <p>Loading...</p>

    return (
        <Row>
            <Col md={8}>
                <h1>Shopping Cart</h1>
                {cartItems.length === 0 ? (
                    <Message variant='info'>
                        Your cart is empty <Link to='/'>Go Back</Link>
                    </Message>
                ) : (
                        <ListGroup variant='flush'>
                            
                        </ListGroup>
                    )}
            </Col>
        </Row>
    )
}
user_124727360

add a default value for your cartItems like an empty array in reducer or do this:

(cartItems || []).length === 0
user_116570210

Your cartItems variable is probably null in the store. Try to initialize it as empty array instead.

user_123091140
Related