As I have been browsing Stack Overflow questions, I’ve noticed that many bugs are due to trying to access a state value after setting it.
An example question on Stack Overflow.
I’ve stumbled many times for being unaware of
setState being an asynchronous operation.
How do we access the state value right after setting it then?
Here is the code that shows accessing a state value (
clickCounts) right after setting it synchronously.
And let’s see the logical error.
console.log doesn’t have access to updated state value even though the call is made after
setState is an operation, you can just wait till the value is set by React.
You might wait for a certain period to access the updated state using
Tada 🎉. It works right?
Yes but No, at this point, you are just praying 🙏) that
setState finishes before accessing the state within
And also, you need to persist the event to be able to access event argument as shown in line#2 (
Refer to Event Pooling for e.persist.
There are two ways as mentioned in the official React documentation.
- Using a callback passed to
componentDidUpdatelife cycle method
Let’s go over them both.
setState has the following signature.
The callback is called after the state has updated using
updater method thus the callback has access to the updated
Here is the updated code & the demo.
React documentation “generally recommends” using
I haven’t been able to find the reason for it, but my guess is because
componentDidUpdate has access to the previous props and previous state (as well as being called before the callback as my demo shows).
Here is the code using
And this demo shows that
- has the access to the updated state value.
- is called before the setState’s callback method.
Frankly speaking, I’ve only used the callback to access updated value because I only found out about the recommended way of using
componentDidUpdate while writing this blog 😝).
And you can play around with the demo on CodeSandBox.