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?
😬 Reproducing the Problem
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
.
😒 Workaround (Not Recommended)
As 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
setTimeout
.
Tada 🎉. It works right?
Yes but No, at this point, you are just praying 🙏) that setState
finishes before accessing the state within setTimeout
.
And also, you need to persist the event to be able to access event argument as shown in line#2 (e.persist()
).
Refer to Event Pooling for e.persist.
😄 Recommend Ways
There are two ways as mentioned in the official React documentation.
- Using a callback passed to
setState
. - Using
componentDidUpdate
life cycle method
Let’s go over them both.
1. Using a callback passed to setState
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 this.state
.
Here is the updated code & the demo.
2. Using componentDidUpdate
life cycle method
React documentation “generally recommends” using componentDidUpdate
.
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 componentDidUpdate
.
And this demo shows that componentDidUpdate
- has the access to the updated state value.
- is called before the setState’s callback method.
👋 Parting Words
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.
The post Accessing React State right after setting it appeared first on Sung's Technical Blog.