This course will be retired on March 31, 2024. We recommend "React Basics" for up-to-date content.
Use Keys to Keep Track of Elements3:58 with Guil Hernandez
React manages what gets rendered to the DOM. In order for this process to be fast and efficient, React needs a way to quickly know which items were changed, added, or removed. For this, React gives elements a special built-in prop named
key. A key is a unique identifier that gives React a way to quickly and reliably identify an element in a list.
React does not recommend using index for unique keys, because the index might not always uniquely identify elements. It's usually best to use a unique id.
According to the React docs:
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.
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