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Start your free trialChris Holder
Full Stack JavaScript Techdegree Graduate 19,841 PointsWhy don't we mutate prevState instead of this.state when we change the value of isRunning?
I thought we weren't supposed to mutate this.state with setState because React sometimes batches state changes and so we should pass a function with prevState to setState instead?
1 Answer
Gabbie Metheny
33,778 PointsIt looks like the React docs recommend setting state using a callback and the previous state, but they do mention you can do it the way Guil has here, too (as a "shallow merge of stateChange
into the new state")-- and looking back, we're using the same method of setting state with an object (as opposed to a callback) in AddPlayerForm
. It seems like generally, for simpler, smaller state updates (i.e. just change one value, as opposed to updating a large array), this shallow merge approach is sufficient because you're unlikely to get out of sync with the UI. You certainly could refactor this to use a callback, though!
*** EDIT ***
In the next video, we end up adding the callback to update based on prevState
as we add more functionality to the Stopwatch!
Chris Holder
Full Stack JavaScript Techdegree Graduate 19,841 PointsChris Holder
Full Stack JavaScript Techdegree Graduate 19,841 PointsThanks, Gabbie! Yep he ends up refactoring to use the new callback method anyway.