Finding an index in an array of objects with 3 possible outcomes

Question

currentUserPosts will have a post object with an id that either matches a tempId, an Id, or nothing.

If there's a tempId match there won't be an id match and vice versa.

This code works but there's something about it I don't like. How can it be refactored?

let postIndex;
postIndex = currentUserPosts.findIndex(post => post.id === upsertParams.tempId);
if (postIndex === -1) {
  postIndex = currentUserPosts.findIndex(post => post.id === upsertParams.id);
}
if (postIndex === -1) {
  currentUserPosts.push(upsertParams);
} else {
  currentUserPosts[postIndex] = upsertParams;
}

Complete function:

const upsertIntoApolloCache = (upsertParams) => {
  try {
    const data = client.readQuery({
      query: USER_POSTS_QUERY,
    });
    const currentUserPosts = data.currentUser.posts;

    const postIndex = currentUserPosts.findIndex(
      post => post.id === upsertParams.tempId || post.id === upsertParams.id
    );
    if (postIndex === -1) {
      currentUserPosts.push(upsertParams);
    } else {
      currentUserPosts[postIndex] = upsertParams;
    }

    client.writeQuery({
      query: USER_POSTS_QUERY,
      data,
    });
  } catch (error) {
    console.log('!!ERROR in upsertIntoApolloCache!!', error);
  }
};

hjpotter92 · Accepted Answer · 2018-06-24 18:17:31Z

3

You can group the two conditions for finding into a single || condition, since the post.id can match only one of tempId or id.

let postIndex = currentUserPosts.findIndex(post => {
  return post.id === upsertParams.id || post.id === upsertParams.tempId
});

if (postIndex === -1) {
  currentUserPosts.push(upsertParams);
} else {
  currentUserPosts[postIndex] = upsertParams;
}

You could, if possible, also change the currentUserPosts from array to a dictionary mapping your post.id to the post itself. This entirely depends on your further usage of the currentUserPosts across application.

Based on updated question content:

let currentUserPosts = {}
for (let post of data.currentUser.posts) {
  currentUserPosts[post.id] = post
}

This way, you'd only have to check against id using the in operation:

let newId = upsertParams.id || upsertParams.tempId
if (newId in currentUserPosts)
  // do unspeakable things

edited Jun 24, 2018 at 18:17

answered Jun 24, 2018 at 9:52

hjpotter92

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\$\begingroup\$ Looks to me like you are missing a return in your findIndex method. \$\endgroup\$

Gerrit0
– Gerrit0

2018-06-24 16:02:58 +00:00
Commented Jun 24, 2018 at 16:02
\$\begingroup\$ Ha!! That was an easy one. Thanks @hjpotter92! Regarding your second suggestion. Don't completely understand what you're getting at. I'll update my questions with the full function so you can see. It probably doesn't matter because I don't have control of the structure. It's a cache object provided by Apollo. \$\endgroup\$

GollyJer
– GollyJer

2018-06-24 16:05:14 +00:00
Commented Jun 24, 2018 at 16:05

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