Welcome to the Treehouse Community

Want to collaborate on code errors? Have bugs you need feedback on? Looking for an extra set of eyes on your latest project? Get support with fellow developers, designers, and programmers of all backgrounds and skill levels here with the Treehouse Community! While you're at it, check out some resources Treehouse students have shared here.

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and join thousands of Treehouse students and alumni in the community today.

Start your free trial

JavaScript React by Example Building the Application Building the GuestList Component

Trevor Maltbie
seal-mask
.a{fill-rule:evenodd;}techdegree seal-36
Trevor Maltbie
Full Stack JavaScript Techdegree Graduate 17,021 Points
Posted by Trevor Maltbie
.a{fill-rule:evenodd;}techdegree seal-36
Trevor Maltbie
Full Stack JavaScript Techdegree Graduate 17,021 Points

Unique Key Should Not Be Index

I have been under the impression that the unique key for each item in this.state should not be the index of the item but rather it's on unique id.

https://medium.com/@robinpokorny/index-as-a-key-is-an-anti-pattern-e0349aece318

However, in this video the teacher makes the key = index.

Is this video outdated or will this be covered later?

1 Answer

Michael Cook
seal-mask
.a{fill-rule:evenodd;}techdegree seal-36
Michael Cook
Full Stack JavaScript Techdegree Graduate 28,975 Points
Michael Cook
.a{fill-rule:evenodd;}techdegree seal-36
Michael Cook
Full Stack JavaScript Techdegree Graduate 28,975 Points

It is possible to use an index as a key, React just doesn't recommend it. From the React website:

"We don’t recommend using indexes for keys if the order of items may change. This can negatively impact performance and may cause issues with component state. Check out Robin Pokorny’s article for an in-depth explanation on the negative impacts of using an index as a key. If you choose not to assign an explicit key to list items then React will default to using indexes as keys."

You can read more about lists and keys here