Course Content

Course Content


The indexOf() method returns the position of a value in a string's first occurrence. If the value cannot be retrieved, the indexOf() method returns -1.

Reordering an item alters the index if the key is an index. As a result, the component state may become jumbled, and the old key may be used for a different component instance. React can't tell if an element was removed or merely the content was updated without a unique key.

indexOf returns the first index in the array where a specified element can be found, or -1 if it does not exist. So index is simply the counter's index in counters. You're making a comparison between an object (counter) and a number ( index ).

  • The indexOf() method is used for a single-dimensional array of primitive datatypes such as string, number, and so on.
  • When looking for an index value from an object element, the findIndex() method is used.

Recommended Courses

Share With Friend

Have a friend to whom you would want to share this course?

Download LearnVern App

App Preview Image
App QR Code Image
Code Scan or Download the app
Google Play Store
Apple App Store
598K+ Downloads
App Download Section Circle 1
4.57 Avg. Ratings
App Download Section Circle 2
15K+ Reviews
App Download Section Circle 3
  • Learn anywhere on the go
  • Get regular updates about your enrolled or new courses
  • Share content with your friends
  • Evaluate your progress through practice tests
  • No internet connection needed
  • Enroll for the webinar and join at the time of the webinar from anywhere