CODEWITHSUNDEEP
javascriptarrays
uzaysan
uzaysan

Reputation: 605

How to check value when using map?

I'm converting some objects to JSON:

const tpL = results.map(post => ({
    ...post.toJSON(),
    postid: post.get("comment").id,
    commentid: post.get("post").id
  }));

But post.get("comment") or post.get("post") is not defined in every obejct. So I have to check if post.get("comment") is exist first.

How can I do that?

Upvotes: 0

Views: 57

Answers (4)

Christian
Christian

Reputation: 1260

The other answers work and are elegant but you might miss that you can also use a full block of code as the body of the function you pass to map() and not just an expression (which ({ /*code omitted*/ })) is. So you could also write

const tpL = results.map(post => {
   const res = post.toJSON();
   if (post.get("comment")){
      res.postid = post.get("comment").id;
   }
   if (post.get("post")){
      res.commentid = post.get("post").id;
   }
   return res;
});

Upvotes: 1

Erazihel
Erazihel

Reputation: 7615

Since Optional Chaining is not supported in every environments nor every Browsers, I'd suggest you to do as follow:

const tpL = results.map(post => ({
    ...post.toJSON(),
    ...(post.get("comment") && { postid: post.get("comment").id }),
    ...(post.get("post") && { commentid: post.get("post").id })
  }));

This way the objects of the array will contain the postid only if .get("comment") is defined and the commentid only if .get('post') is defined.

Upvotes: 2

mfelixson
mfelixson

Reputation: 56

const tpL = results.map(post => ({
    ...post.toJSON(),
    postid: post.get("comment") ? post.get("comment").id : null,
    commentid: post.get("post") ? post.get("post").id : null
  }));

PS note the return value adjusts to your defaults This is similar to the solution above but allows you to set defaults

Upvotes: 1

CertainPerformance
CertainPerformance

Reputation: 371233

This sounds like a great use case for optional chaining:

const tpL = results.map(post => ({
    ...post.toJSON(),
    postid: post.get("comment")?.id,
    commentid: post.get("post")?.id
}));

If the .get returns null or undefined, the resulting property value will undefined.

This is relatively new syntax, so it's not supported everywhere yet. (if you're putting this on a public website, hopefully your script is already being transpiled with Babel for cross-browser compatibility)

Upvotes: 5

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