What does ReactDOM.render() first argument typically contain?

What does ReactDOM.render() first argument typically contain?

• A. A DOM node
• B. A plain text string
• C. A JSX expression to be rendered to the screen
• D. An array of elements

Answer: (C)

React rendering starts from a description of the UI, not a real DOM node. The first argument to ReactDOM.render is a React element, which is an object that describes what React should render. Using JSX is the common way to create that element, because JSX is syntax that compiles to React.createElement calls, producing the element tree that React uses to build and manage the UI. The second argument is the actual DOM node that will host that UI. So you typically pass a JSX expression like <App /> as the first argument to render, because it represents the UI you want React to render. Plain strings or arrays aren’t used as the top-level input in most cases—the top level is a single React element whose children can be composed of strings or arrays inside the element.

React rendering starts from a description of the UI, not a real DOM node. The first argument to ReactDOM.render is a React element, which is an object that describes what React should render. Using JSX is the common way to create that element, because JSX is syntax that compiles to React.createElement calls, producing the element tree that React uses to build and manage the UI. The second argument is the actual DOM node that will host that UI. So you typically pass a JSX expression like as the first argument to render, because it represents the UI you want React to render. Plain strings or arrays aren’t used as the top-level input in most cases—the top level is a single React element whose children can be composed of strings or arrays inside the element.