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Understanding Synthetic Events in React

Let's look at synthetic events in React, their benefits for event handling across browsers, basic usage, and importance for performance and coding ease.


Synthetic events in React are a key feature for anyone looking to master this popular JavaScript library. The ability to create interactive and dynamic user interfaces depends largely on how efficiently you can handle events such as clicks, input changes, or keystrokes. The topic seems simple, but the deeper you delve into it, the more you realize that there is much more under the hood.

Going into detail not only introduces you to the concept but also gives you practical skills. This, in turn, allows you to create applications that are not only interactive, but also efficient and reliable. As you go through this article, remember that the main idea is to help you write code that is easy to maintain, efficient, and most importantly, provides a seamless user experience.

What are synthetic events?

The core of a synthetic event in React is a cross-browser wrapper around a native browser event. What does it mean? Simply put, React creates its own event object that wraps around the browser's native event object, thus providing consistency. By doing this, React avoids the need to handle cross-browser differences in event handling code.

In terms of functionality, synthetic events offer the same interface as native events. You have regular methods like preventDefault , and properties like target . However, React controls these synthetic events directly in React components, not in the DOM. This is critical because it allows React to merge updates and improve performance, as we'll discuss in the following sections.

The Need for Synthetic Events

One might ask why React decided to develop a separate event system instead of sticking with native browser events. The main reason is to eliminate inconsistencies that different browsers have with their native event implementations. For example, event names and properties are not standardized between browsers, and even something as simple as a mouse click can behave differently on different platforms.

By introducing synthetic events, React eliminates these inconsistencies. It's like a translation service that ensures that every browser speaks the same language, at least as far as events are concerned. With synthetic events, the properties and methods of the event object remain stable, eliminating browser-specific checks in your code.

Basic usage and syntax

Implementing synthetic events in your React application is quite simple. The JSX you write in your components directly corresponds to the type of synthetic event you want to handle.For example, the attribute onClick corresponds to a click event. It's worth noting that these attributes are case sensitive, so you should use camelCase rather than lowercase or hyphenated names.

Here is an example with some code for better understanding. Imagine you have a button and you want to execute the handleClick function when the button is clicked.

// Example of a click event in a React component

The handleClick function automatically receives a SyntheticEvent object from React and you can operate them in the body of the function.

Properties of Synthetic Events

SyntheticEvent objects in React have many useful properties. These include bubbles, cancellable, currentTarget and so on. For example, you can use to directly interact with the DOM element that raised the event. You can retrieve a value from an input field or change the element's class.

It's also worth noting that all event properties and values ​​are stored in the event pool. This is done to improve performance since React can reuse event objects.

Event Pooling

One of the unique aspects of working with synthetic events in React is that they undergo something called "pooling". This means that event objects will be cleaned up and reused after the events are processed. This is done to optimize performance and reduce the load on garbage collection.

What does this mean in practice? If you try to access event properties asynchronously or after the event has already been processed, you will see that all properties will become null . You will either need to use event.persist() to persist the properties, or, what most often happens, copy the desired properties to variables inside the event handler.

Event Delegation

In React, event delegation is a built-in feature that makes event handling efficient. Instead of assigning handlers to each individual element, React uses a single handler at the top level. When an event occurs, it determines which component is the source and calls the appropriate handler.

This means that you don't need to explicitly bind or unbind event handlers in most cases. React does this automatically, which reduces code and improves performance.

Event Composition

Synthetic events in React also support the concept of event composition. This means that you can create more complex handlers by combining different event types.For example, you can react to the onMouseDown and onMouseUp events at the same time to create your own drag-n-drop event.

Interacting with browser events

Sometimes you may need to interact with native browser events. Synthetic events offer the ability to access a native event through the nativeEvent property. It allows you to control the native event directly if necessary for your application.

Mouse and Keyboard Events

React provides various synthetic mouse and keyboard events such as onClick , onDoubleClick , onBlur and so on. For keyboard related events, there are synthetic events like onKeyDown , onKeyPress , onKeyUp which help in capturing keystrokes.

For example, if you want to perform some logic when the Enter key is pressed, you can do this by examining the event.key or event.keyCode properties in your event handler.


Understanding synthetic events in React is a key aspect when creating interactive and robust applications. They serve as an abstraction layer over native browser events and offer a unified way to handle user interactions across browsers. From basic usage to more advanced topics like event pooling and delegation, knowing how synthetic events work can greatly optimize your React applications and make your code more maintainable.

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