Understanding the React Source Code - UI Updating (Transactions) VII
In this article, we'll dive deep into how React updates the user interface by exploring the Transactions module. This module is responsible for managing the updating process and ensuring that everything runs efficiently.
Transactions
A transaction in React is a set of operations that must be executed as a single unit. Transactions are used to ensure that all updates to the user interface are consistent and predictable. They also help reduce the number of unnecessary updates.
Transactions are managed by the Transaction class, which provides three methods for controlling the transaction:
perform: This method takes a function and executes it within a transaction.rollback: This method is called when a transaction is aborted or fails. It undoes any changes made during the transaction.initializeAll: This method initializes all transactions at the beginning of a new update cycle.
The Update Queue
When a component's state changes, React schedules an update to the component's user interface. These updates are added to a queue, which is managed by the ReactUpdates module.
The ReactUpdates module provides two methods for managing the update queue:
enqueueUpdate: This method adds an update to the queue.batchedUpdates: This method takes a function and executes it within a transaction.
When batchedUpdates is called, React creates a new transaction, executes the function within the transaction, and then commits the transaction. If any updates were scheduled during the execution of the function, they are processed as part of the same transaction. This helps reduce the number of expensive DOM operations needed to update the user interface.
Let's take a look at an example:
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-In the handleClick method, we call setState twice with the same key (count). If React didn't batch these updates together, the user interface would be updated twice unnecessarily. However, because we called setState within a batchedUpdates call, React will only update the user interface once.
Conclusion
Understanding how transactions work in React is crucial for developing efficient and predictable user interfaces. By managing updates with transactions, React can ensure that changes to the user interface are consistent and reduce the number of expensive DOM operations needed to update the UI.
In our next article, we'll dive deeper into how the ReactReconciler module handles the actual updating of the user interface.
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