One of the advanced features of React is that it allows arbitrary user interface (UI) content to be passed into the component using properties. As compared to React”s special children property, which allows only a single user interface content to be passed into the component, this option enables multiple UI content to be passed into the component. This option can be seen as an extension of children property. One of the use cases of this option is to layout the user interface of a component.

For example, a component with customizable header and footer can use this option to get the custom header and footer through properties and layout the content.

Example

A quick and simple example with two properties, header and footer is given below

<Layout header={<h1>Header</h1>} footer={<p>footer</p>} />

And the layout render logic is as follows −

return (<div>
   <div> 
      {props.header} 
   </div> 
   <div> 
      Component user interface 
   </div> 
   <div> 
      {props.footer} 
   </div> 
</div>)

Let us add a simple header and footer to our expense entry list (ExpenseEntryItemList) component.

Open expense-manager application in your favorite editor.

Next, open the file, ExpenseEntryItemList.js in src/components folder.

Next, use header and footer props in the render() method.

return (
   <div> 
      <div>{this.props.header}</div> 
         ... existing code ... 
      <div>{this.props.footer}</div> 
   </div> 
);

Next, open index.js and include header and footer property while using the ExpenseEntryItemList component.

ReactDOM.render(
   <React.StrictMode>
      <ExpenseEntryItemList items={items}
         header={
            <div><h1>Expense manager</h1></div>
         }
         footer={
            <div style={{ textAlign: "left" }}>
               <p style={{ fontSize: 12 }}>Sample application</p>
            </div>
         } 
      />
   </React.StrictMode>,
   document.getElementById(''root'')
);

Next, serve the application using npm command.

npm start

Next, open the browser and enter http://localhost:3000 in the address bar and press enter.

Sharing logic in component aka Render props

Render props is an advanced concept used to share logic between React components. As we learned earlier, a component can receive arbitrary UI content or React elements (objects) through properties. Usually, the component render the React elements it receives as is along with its own user interface as we have seen in children and layout concept. They do not share any logic between them.

Going one step further, React allows a component to take a function which returns user interface instead of plain user interface object through properties. The sole purpose of the function is to render the UI. Then, the component will do advanced computation and will call the passed in function along with computed value to render the UI.

In short, component”s property, which accepts a JavaScript function that renders user interface is called Render Props. Component receiving Render Props will do advanced logic and share it with Render Props, which will render the user interface using the shared logic.

Lot of advanced third-party library are based on Render Props. Some of the libraries using Render Props are −

• React Router
• Formik
• Downshift

For example, Formik library component will do the form validation and submission and pass the form design to the calling function aka Render Props. Similarly, React Router do the routing logic while delegating the UI design to other components using Render Props.