findIndex() Method in JavaScript

The findIndex() method in JavaScript is used to find the index of the first element that matches a specific condition.
It is similar to the find() method, but instead of returning the element itself, it returns the index of that element.
If no element satisfies the condition, findIndex() returns -1.

How `findIndex()` Works:

The method takes a callback function that is executed for each element.
If the condition is satisfied, it returns the index of the first matching element.
If no match is found, it returns -1.

Example:

We have a blogs array containing some blog posts with id, title, and description:

const blogs = [
    { id: 1, title: 'Title-1', description: 'Description-1' },
    { id: 2, title: 'Title-2', description: 'Description-2' },
    { id: 3, title: 'Title-3', description: 'Description-3' }
];

Using findIndex() to Locate a Blog by ID:

We want to find the blog with id = 2 using findIndex().

function foundBlog(blogId) {
    return blogs.findIndex(blog => blog.id === blogId);
}

Here:

The findIndex() method iterates over the blogs array to locate the first blog with the matching id (in this case, id: 2).
The index of the blog is returned by the function.

Checking the Index:

We store the result of the function in foundIndex:

const foundIndex = foundBlog(2);

Displaying the Blog:

We check if the index is not -1, which means the blog was found. If found, we print the blog details, otherwise, we display "Blog not found":

if (foundIndex !== -1) {
    document.write(`
        Title: ${blogs[foundIndex].title}, <br>
        Description: ${blogs[foundIndex].description}
    `);
} else {
    document.write("Blog not found!");
}

Output:

If the blog is found, the output will be:

Title: Title-2, 
Description: Description-2

If no matching blog is found:

Blog not found!

Summary:

The findIndex() method is useful for finding the index of an element based on a condition.
It returns -1 if no matching element is found.
The method is ideal when you need the position of an element, rather than the element itself.

findIndex() Method in JavaScript

findIndex() Method in JavaScript

How `findIndex()` Works:

Example:

Using findIndex() to Locate a Blog by ID:

Checking the Index:

Displaying the Blog:

Output:

Summary:

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findIndex() Method in JavaScript

How findIndex() Works:

Example:

Using findIndex() to Locate a Blog by ID:

Checking the Index:

Displaying the Blog:

Output:

Summary:

Related Articles

map() Methods in JavaScript

slice() Methods in JavaScript

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How `findIndex()` Works: