When to use JSX.Element vs ReactNode vs ReactElement?

When building user interfaces in React projects, we frequently encounter several core concepts: JSX Element, ReactNode, and ReactElement. I will explain each concept in turn and provide usage scenarios.

JSX Element

JSX (JavaScript XML) is a syntax extension for React that enables us to write HTML-like markup directly in JavaScript. When we write code like <div>Hello World</div>, we are creating a JSX Element.

Usage Scenarios:

• Direct UI Rendering in Components: The most common use case is when rendering UI layouts within functional or class components.

  jsx
  function Welcome() {
    return <div>Welcome to React</div>;
  }

• Conditional Rendering: When displaying different UI elements based on conditions, we typically use JSX Elements.

  jsx
  function Greeting({ isUserLoggedIn }) {
    return isUserLoggedIn ? <div>Welcome back!</div> : <div>Please sign in.</div>;
  }

ReactNode

ReactNode is a type in React's type system that can represent strings, numbers (as text), JSX elements, JSX Fragments, null, or undefined, or even arrays of these types. It is primarily used for type definitions to ensure components can handle various types of children or values.

Usage Scenarios:

• As Props or Child Components: When creating reusable components, we can define the child prop type as ReactNode to accept multiple types of child elements.

  tsx
  type CardProps = {
    children: React.ReactNode;
  };
  
  function Card({ children }: CardProps) {
    return <div className="card">{children}</div>;
  }

• Rendering Dynamic Content: When rendering content of uncertain types, using ReactNode makes components more flexible.

  tsx
  const content: React.ReactNode = getContent(); // getContent may return string, element, or null
  return <div>{content}</div>;

ReactElement

ReactElement is an abstraction of JSX Element, representing objects created by the React.createElement() function. Once JSX is compiled, each JSX element is converted into a ReactElement.

Usage Scenarios:

• Creating Elements with createElement: When working in environments without JSX syntax, we can use React.createElement to create elements.

  jsx
  function Button() {
    return React.createElement('button', null, 'Click me');
  }

• Type Definition: When specifying that a variable or function return value must be a React element.

  tsx
  function getHeaderElement(): React.ReactElement {
    return <h1>Header</h1>;
  }

In summary:

• JSX Element is the HTML-like code we write to declaratively describe UI.
• ReactNode is a type definition covering almost all renderable content types.
• ReactElement is the underlying object created by React.createElement(), representing the compiled JSX element.

Developers should choose when to use these types based on specific scenarios, leveraging TypeScript or PropTypes type systems. This helps ensure component reusability, maintainability, and consistent type handling across different contexts.