为什么我没有取回 useState 的新值 - React.JS？

Question

In the line setVotedPosts([...previousVotedPosts, postId]);

I'm trying to get the previous value of votedPosts, but I'm getting back the newest value.

full code : https://github.com/silvertechguy/reddit-clone/blob/main/src/components/vote-buttons.js

App live : https://reddit-clone-official.vercel.app/

const VoteButtons = ({ post }) => {
  const [isVoting, setVoting] = useState(false);
  const [votedPosts, setVotedPosts] = useState([]);

  useEffect(() => {
    const votesFromLocalStorage =
      JSON.parse(localStorage.getItem("votes")) || [];

    setVotedPosts(votesFromLocalStorage);
  }, []);

  const handleDisablingOfVoting = (postId) => {
    const previousVotedPosts = votedPosts;
    setVotedPosts([...previousVotedPosts, postId]);

    localStorage.setItem(
      "votes",
      JSON.stringify([...previousVotedPosts, postId])
    );
  };

  const handleClick = async (type) => {
    setVoting(true);

    // Do calculation to save the vote.
    let upVotesCount = post.upVotesCount;
    let downVotesCount = post.downVotesCount;

    const date = new Date();

    if (type === "upvote") {
      upVotesCount = upVotesCount + 1;
    } else {
      downVotesCount = downVotesCount + 1;
    }

    await db.collection("posts").doc(post.id).set({
      title: post.title,
      upVotesCount,
      downVotesCount,
      createdAt: post.createdAt,
      updatedAt: date.toUTCString(),
    });

    // Disable the voting button once the voting is successful.
    handleDisablingOfVoting(post.id);

    setVoting(false);
  };

  const checkIfPostIsAlreadyVoted = () => votedPosts.includes(post.id);

Answer 1

Problem

const previousVotedPosts = votedPosts;

In JavaScript, arrays are reference types, so you can't just create a new copy of an array using = .

Try this solution

Clone array using spread syntax( ... ).

  const handleDisablingOfVoting = (postId) => {
    const previousVotedPosts = [...votedPosts];
    setVotedPosts([...previousVotedPosts, postId]);

    localStorage.setItem(
      "votes",
      JSON.stringify([...previousVotedPosts, postId])
    );
  };