Question 115986 in Mongodb Question posted in
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Mongodb – Uncaught TypeError: Cannot read properties of undefined (reading 'map') while using map function in useEffect

useEffect(() => {
        if(currentUser){
            currentUser?.friends.map(friends => {
                if(friends._id===currentProfile._id){
                    return setFriend(true)
                }
            })
        }else{
            return setFriend(false)
        }
    },[currentUser,currentProfile])

//currentUser is the user logged in
//currentProfile is user selected

i want to show button as Unfriend if the user selected is already a friend.Iam trying to use a map function to find if the user is already a friend.but the map function is shown as error

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2

Answers


  1. 0

    Looks to me like currentUser is defined but doesn’t have a property currrentUser.friends.
    Try currentUser?.friends?.map(...)

    And change the else clause to always return instead. If return setFriend(true) was called, the return friend(false) won’t be called, but in all other cases.

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  2. 0

    Since you have the if statement we already know that currentUser exists you will have to see if the currentUser have friends.
    However map should be used to create a new array, you use it to iterate over friends. You could simplify the whole useEffect with some instead

    useEffect(() => {
  setFriend(
    currentUser &&
      currentUser.friends?.some((friends) => friends._id === currentProfile._id)
  );
}, [currentUser, currentProfile]);

    If currentUser is a value and a friend have the same id as currentProfile

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