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Event system is one of the most useful features of the React framework.

In particular, onChangethe event is one of the most commonly handled events in React. It is based on the well-known onchangeproperty in vanilla JavaScript, but the event in React onChangeincludes some additional features.

It is also written in camelCase to help developers distinguish it from regular JavaScript events.

Understanding onChangehow events work can help you write more powerful dynamic forms.

In React, onChangeevents occur when a user's input changes in any way. The input might change when the user enters additional text, selects a different option, unchecks a checkbox, or other similar situations.

Imagine 布尔值a situation when you have a checkbox input and you need to store the user's choice (value) in the state. In this case, onChangeit will be very useful. Every time the user changes his mind and unchecks it, the state will be updated.

Here is an example:

return (
		<input type="checkbox" onChange={(e) => this.setState("status": e.target.value)}/> 
		)

This is a onChangesimple demonstration of how useful events are.

We make this element a controlled input by storing the input value in our component state. This term describes an 状态input whose internal state is merged with a React component to provide a single source of truth.

Note that in JSX, JavaScript expressions need to be placed between two curly braces. We can also define the handler separately and call it inside the curly braces.

For example:

<input type="checkbox" onChange={(e) => handleChange(e)}/> 

For more complex handler functions, this would be a more readable approach.

In some cases, you may need to bypass the default behavior and trigger onChangethe event manually.

Imagine the browser autofills your password so onChangethe will not fire, but you need it to perform the animation. In this case, you have to trigger it manually onChange.

To avoid duplicate instances of the same event, React sometimes intentionally swallows some events and doesn't execute them. The solution is to use native value setters setNativeValue().