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JavaScript React by Example Building the Application Building the GuestList Component

Trevor Maltbie
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Trevor Maltbie
Full Stack JavaScript Techdegree Graduate 16,996 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Is this video outdated or will this be covered later?

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