在控制台中获取未定义 - React.js

Question

So, the request is returning the JSON file. But when in console it is saying 'Undefined' and I do not know why.

So the button when clicked will send the results from my request from the google Place API; which contains the place_id needed to make the call to the Place Details API to the Info component.

const OnButtonClick = (restaurant) => {
        setRestaurant(restaurant)
        setOpenPopup(true)
    }

<button className="cardButton" onClick={() => OnButtonClick(restaurantData)}>
    View Information
</button>
<InfoPopup open={openPopup} restaurant={restaurant} onClose={() => setOpenPopup(false)} />

So, this works the way I think it does (Sorry, I am new to React)

Here's the InfoPopup component

function InfoPopup({ open, onClose, restaurant }) { 
    const [restaurant1, setRestaurant1] = useState([])

    let id = restaurant.place_id
    let URL = `/maps/api/place/details/json?place_id=${id}&key=${process.env.REACT_APP_API_KEY}`
    const fetchRestaurants1 = async () => {
        const res1 = await axios.get(URL)
        setRestaurant1(res1.data.results);
      }

    useEffect(() => {
          fetchRestaurants1()
          console.log(restaurant1) //This is getting 'Undefined' 
      }, [id]);
        

    const navigate = useNavigate()
    if (!open) {return null}
   

    return ReactDOM.createPortal(
    <>
        <div>
            {restaurant1?.map(restaurant => (
                <div key={restaurant.place_id}> {restaurant.formatted_phone_number} </div>
            ))}
        </div>
        <div className="popup">
            <div className="popup-inner">
                <button className="close-btn" onClick={onClose}> Close </button>
                <h1 className="title"> {restaurant.name} </h1>
            <ul>
                {/* <li className="service">
                    Status: {}
                </li> */}
                <li className="location">
                    Address: {restaurant.vicinity}
                    Phone Number: 
                </li>
                <li className="cost">
                    Cost: {restaurant.price_level}
                </li>
                {/* <li className="food">
                    Food Type:
                </li> */}
            </ul>
            <div className="links">
                <Link className="writeButton" to="/write" state={{data: restaurant}}>
                    Write a review
                </Link>
                {/* <button className="writeButton" onClick={() => navigate("/write", {data:restaurant})}>
                    Write a review
                </button> */}
                <Link className="readButton" to="/read" state={{data: restaurant}}>
                    Read the reviews
                </Link>
                {/* <button className="readButton" onClick={() => navigate("/read")}>
                    Read the reviews
                </button> */}
            </div>
            </div>
        </div>
    </>,
    document.getElementById('portal')
  )
}

I think the problem is on the first render, there's no ID being passed. But I do not know how to work around it. Any help would be appreciated.

Answer 1

Looking at this block of code:

 const fetchRestaurants1 = async () => {
    const res1 = await axios.get(URL)
    setRestaurant1(res1.data.results);
  }

useEffect(() => {
      fetchRestaurants1()
      console.log(restaurant1) //This is getting 'Undefined' 
  }, [id]);

You're awaiting the result of the GET call, which is good, because it allows you to set state in the next line after waiting for the response.

The problem: when you call fetchRestaurants1() in the useEffect(), you're not waiting for that function to execute, therefore, we jump straight to the next line and console.log() restaurant1 , which is of course still blank.

The same issue arises with set state calls. If you do:

const [value, setValue] = useState(null);

then sometime later:

setValue(5);
console.log(value);

The value posted to console will be null, because JS doesn't want to wait for the set state call to finish before moving onto the next line, console.log(value);

To fix this: make the useEffect callback async, and await the functions in which you're making your axios.get calls. Example:

  const fetchSomeData = async () => {
    const response = await axios.get(URL);
    setData(response.data);
  }

  useEffect(async () => {
      await fetchSomeData();
      /* do some stuff */
  }, []);

Of course, you still can't console.log after the set state call above.

If you want a generalizable way to log state changes without worrying about async behavior, you can add a simple useEffect:

  useEffect(() => {
    console.log(value);
  }, [value]);

Where value is any state variable. Since value is in the dependency array, anytime it changes, the useEffect will fire and log the change.