⚛️ Explaining React's Types

React's type system, when used with TypeScript, provides developers with a robust framework for building type-safe applications. Understanding the nuances between various React types is crucial for making informed decisions about their usage. Let's dive into a detailed comparison of these types in pairs to understand their differences and appropriate use cases.

1️⃣ React.FC vs React.ElementType

React.FC (React.FunctionComponent)

React.FC is a type specifically used for defining function components in React. It started to become more popular when React Hooks were introduced and widely adopted.

Prior to React 18, it used to include an implicit children prop, making it suitable for components expected to have children. For a long time, though, the implicit children prop type has been removed according to React 18's type changes.

Here's a usage example:

interface SomeComponentProps {
  title: string;
  children?: React.ReactNode;
}

export const SomeComponent: React.FC<SomeComponentProps> = ({ title, children }) => {
  return (
    <article>
      <h2>{title}</h2>

      {children}
    </article>
  );
};

However, since the removal of the implicit children prop type, much fewer people use React.FC now as it's clunky and provides no real benefits compared to directly assigning the interface to the props object:

interface SomeComponentProps {
  title: string;
  children?: React.ReactNode;
}

export const SomeComponent = ({ title, children }: SomeComponentProps) => {
  return (
    <article>
      <h2>{title}</h2>

      {children}
    </article>
  );
};

React.ElementType

React.ElementType, on the other hand, is a broader type that represents any component type that can be rendered by React. This includes not only React functional and class components but also string tags for HTML elements (e.g., 'div', 'span'). React.ElementType is particularly useful when you want to accept a component as a prop and render it, allowing for dynamic component usage.

const DynamicComponent: React.ElementType = 'div';

export const Container = () => (
  <DynamicComponent className="container">Hello, world!</DynamicComponent>
);

Here, DynamicComponent is typed as React.ElementType, allowing it to be dynamically assigned to different types of components or HTML elements.

Comparison notes

• React.FC is mainly for defining functional components. Since React 18, it is not that useful anymore.
• React.ElementType offers more flexibility in accepting various kinds of renderable entities. Use React.ElementType when you need something that can dynamically accept different types of React components or HTML elements.

2️⃣ React.ReactNode vs React.ReactElement vs JSX.Element

React.ReactElement

React.ReactElement is an object with type, props, and key properties, created by the React.createElement() function. It's a more specific type compared to React.ReactNode, representing elements that can be rendered directly by React.

const elementContent: React.ReactElement = <div>Hello, React.ReactElement!</div>;

export const Container = () => <>{elementContent}</>;

React.ReactNode

React.ReactNode is the most inclusive type, representing anything that can be rendered by React. This includes primitive types (strings, numbers, booleans), JSX.Elements, React.ReactElements, arrays of these types, and more. It's the go-to type for props that can accept a wide variety of content, such as children.

const multiElementContent: React.ReactNode = (
  <div>
    <p>This is a paragraph.</p>
    {'This is a text node.'}
    {null}
  </div>
);

const primitiveTypeContent: React.ReactNode = "I'm a primitive-type React.ReactNode";

export const Container = () => {
  return (
    <>
      {multiElementContent}
      {primitiveTypeContent}
    </>
  );
};

This Venn diagram below depicts the relation between React.ReactNode and React.ReactElement:

JSX.Element

JSX.Element is essentially a React.ReactElement with a broader definition, allowing various libraries to implement JSX in their own way. It's the type used internally by TypeScript to represent the return type of JSX expressions.

const jsxElement: JSX.Element = <span>Hello, JSX.Element!</span>;

export const Container = () => <>{jsxElement}</>;

Comparison notes

• React.ReactNode is the most flexible and inclusive, suitable for typing props like children that can accept diverse content.
• React.ReactElement and JSX.Element are more specific, with React.ReactElement being suitable for elements created by React and JSX.Element for elements defined using JSX syntax.

💡 Fun facts

• The returned value of a function component a.k.a. the result of the rendering process is always either React.ReactNode or React.ReactElement/JSX.Element. Basically, a function component can be understood as:

type ReactFC<P = {}> = (props: P) => React.ReactNode;

• Calling the function component just like any regular function gives us the same result as using the JSX syntax, meaning:

const MyComponent = ({ children }: { children: React.ReactNode }) => {
  return <div>{children}</div>;
};

export const App = () => {
  return (
    <div>
      <MyComponent>
        Rendering MyComponent with <strong>JSX Syntax</strong>
      </MyComponent>
    </div>
  );
}

is the same as:

const MyComponent = ({ children }: { children: React.ReactNode }) => {
  return <div>{children}</div>;
};

export const App = () => {
  return (
    <div>
      {MyComponent({
        children: (
          <>
            Rendering MyComponent by 
            <strong>Invoking Function Component</strong>
          </>
        ),
      })}
    </div>
  );
}

Check out the codesandbox below for the demo:

🏁 Conclusion

Understanding the differences between these React types and interfaces allows developers to make more informed decisions, leading to cleaner, more maintainable code. Whether you're defining components, accepting dynamic content, or handling children, choosing the right type is crucial for leveraging React and TypeScript's full potential.

Please look forward to my upcoming articles that dive deeper into the patterns that utilize the understanding of these types.

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