Upcoming React 17 Changes

An overview of React’s upcoming release v17.

React v17 is coming 2.5 years after the release of v16. The React 16 version included many new features including hooks, contexts, error handling, portals, and more. React 17 will not include new features, however, but it does include important changes and improvements to the library itself. These changes give us insight into what the React team is planning for future updates (meaning that they are taking time to make the platform stable and easier to upgrade).

Previously, the React team’s upgrades used to take an all-or-nothing approach, meaning that if you wanted to upgrade React then you had to upgrade everything. In the upcoming version of React, they have changed how it works. React 17 will allow us to use multiple versions at the same time. We will be able to upgrade the whole application piece by piece or at once depending upon the size and complexity of the application. It is still recommended to upgrade the whole application at once and use the single version across whole application.

Here is an example provided by React team for using multiple versions

Following are the proposed changes:

Event Delegation

The earlier versions of React attached events directly at the document level. This caused issues with Event Delegations, especially when multiple versions of React were used simultaneously. In the next version, the event listeners are no longer stored at the very top of the system i.e. document.addEventListener().

Instead, what they have done is make all the event listeners appear on the root node attached through React. This makes it safer to embed React trees managed by one version inside a tree managed by a different version. The benefit of this approach is that the outer application will not have any issues with the events because the events will not propagate all the way to the top level.

Effect Cleanup Timing