CODEWITHSUNDEEP
javascriptfind
Razvan Zamfir
Razvan Zamfir

Reputation: 4684

Why does this use of JavaScript's find() method return undefined?

I ran into this (unexpected) bug while trying to make a JavaScript function that gets a single post by id, from an array of objects:

let posts = [
    {id: 1, title: "Lorem ipsum dolor sit amet"},
    {id: 2, title: "Numquam natus culpa non dignissimos dicta"},
    {id: 3, title: "Tenetur culpa accusamus"}
];

let singlePost;

function findById(array, id) {
  singlePost = array.find(function(post){
    console.log(post.id);
    return post.id === id;
    });
}

singlePost = findById(posts, 2);
console.log(singlePost);

For a reason I have not figured out, console.log(singlePost) outputs undefined.

Where is my mistake?

Upvotes: 0

Views: 71

Answers (3)

danielvalred
danielvalred

Reputation: 21

You are setting a variable without the function returning anything, so replace the assignment of the variable within the function with a return

let posts = [
    {id: 1, title: "Lorem ipsum dolor sit amet"},
    {id: 2, title: "Numquam natus culpa non dignissimos dicta"},
    {id: 3, title: "Tenetur culpa accusamus"}
];

let singlePost;

function findById(array, id) {
  return array.find(function(post){
    return post.id === id;
    });
}

singlePost = findById(posts, 2);
console.log(singlePost);

Upvotes: 1

Razvan Zamfir
Razvan Zamfir

Reputation: 4684

Of course, the function was not returning the singlePost itself. Here is what I should have done:

let posts = [
        {id: 1, title: "Lorem ipsum dolor sit amet"},
        {id: 2, title: "Numquam natus culpa non dignissimos dicta"},
        {id: 3, title: "Tenetur culpa accusamus"}
];

let singlePost;

function findById(array, id) {
  singlePost = array.find(function(post) {
    return post.id === id;
  });
  return singlePost;
}

singlePost = findById(posts, 2);
console.log(singlePost);

Upvotes: 0

nibble
nibble

Reputation: 404

Because your function is returning undefined and you are assigning it to singlePost. You can check below.

findById(posts, 2);
console.log(singlePost); // This will console.log the value of singlePost

Upvotes: 1

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