Choosing Between JSX.Element, ReactNode, and ReactElement

Understanding React Render Types: JSX.Element, ReactNode, and ReactElement

Migrating a JavaScript application to TypeScript can be a rewarding venture. It not only ensures type safety but also introduces an altogether better structuring of code. Recently, during the migration of a React application to TypeScript, I stumbled upon an interesting nuance related to the return types of the render functions in functional components. Initially, I had used JSX.Element as the return type across the board. However, issues cropped up when a component returned null, as null isn’t considered a JSX.Element. My quest for a solution revealed some intricacies between JSX.Element, ReactNode, and ReactElement.

Below, I’ll share the distinctions among these types and explain how to apply them correctly to both class and functional components. Also, I’ll provide a solution for including null in the possible return types of your React components.

1. Understanding the Differences: JSX.Element, ReactNode, and ReactElement

JSX.Element

JSX.Element refers to the type applied for elements written using JSX syntax. This is quite specific – it only includes what results from JSX tag conversions. For instance, <div /> or <MyComponent /> are considered JSX.Elements. If you type a component function’s return as JSX.Element, you declare that it always returns a React element or nothing at all.

ReactNode

ReactNode is a more inclusive type. It covers anything that could be rendered: elements, strings, numbers, fragments, arrays, or even null. Specifically, ReactNode includes JSX.Element, but also includes other values like string, number, null, and undefined, making it a preferred type for return values of rendering functions, especially in contexts where different types of children might be included.

ReactElement

ReactElement, a specific term in React’s type definitions, refers to an object of a type that React can render, which basically contains a type and props. Unlike JSX.Element, ReactElement is created inside React and is associated with rendering logic provided by the library.

2. Different Return Types for Functional and Class Components

Why Different Returns?

In functional components, it’s common to specify ReactElement because they are expected to return a single React element. This fits directly with the nature of functional components that typically have a declaration returning JSX directly.

Class components, however, manage a wider range of rendering possibilities, hence they use ReactNode. In class components, render methods can return null, arrays, strings, and other valid JSX constructs because their structure allows handling these without direct declaration in the return statement of the render method itself.

3. Addressing the null Return Issue

When you have a functional component that might return null or indeed any of the types included in ReactNode, you can address this by either:

• Explicitly typing the return as ReactNode: This works well because it encompasses null, JSX elements, and other types of react renderable outputs.

const MyComponent: React.FC = (): React.ReactNode => {
  return null; // perfectly valid
}

• Using a union type with ReactElement: This method is verbose but makes your intentions clear.

const MyComponent: React.FC = (): ReactElement | null => {
  return null; // perfectly valid
}

Conclusion

In TypeScript, understanding the nuanced differences among JSX.Element, ReactNode, and ReactElement can help clear up confusion and aid in appropriately typing the return values of components. As shown, ReactNode provides the most flexibility for the kinds of values you might want to render in a React application, inclusive of null. Meanwhile, adjusting your functional components to return ReactNode or a union type including ReactElement and null ensures that the components remain correctly typed and capable of handling conditional rendering. This form of meticulous typing is crucial in building robust and sustainable TypeScript-React applications.