JavaScript's Array.map function failing to return a value

Here is a snippet of code from an api endpoint in nextJS that retrieves the corresponding authors for a given array of posts. Each post in the array contains an "authorId" key. The initial approach did not yield the expected results:

const users = posts.map(async (post) => await prisma.user.findUnique({ where: { id: post.authorId }}));

Dissatisfied with the outcome, I decided to try a more traditional method which proved successful:

    const users = []
    for (let i = 0; i < posts.length; i++) {
            const user = await prisma.user.findUnique({
                where: {
                    id: posts[i].authorId,
                },
            });
            users.push(user);
        }

I initially suspected the issue might be related to the arrow syntax or implicit return, so I made adjustments as follows:

        const getUsers = async (post: Post) => {
            const user = await prisma.user.findUnique({
                where: {
                    id: post.authorId,
                },
            });
            console.log(user);
            return user;
        };
        const users = posts.map(getUsers);

Although the user object was successfully logged to the console, it still did not return the expected value, resulting in an array filled with empty objects matching the size of the posts array. Can anyone identify where I may have gone wrong?

Note that in this scenario, I am utilizing Prisma as an ORM.

Answer №1

The two code snippets you provided do not have the same functionality.

When using the getUsers function, it returns a Promise since it is an asynchronous function that resolves with a user. Therefore, in your last example, the variable users contains an array of promises. To achieve your intended outcome, you should consider utilizing the following code snippet:

const users = await Promise.all(posts.map(getUsers));

This allows you to concurrently retrieve all users from the array of promises.

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