Using React Components In SPFx Extension Application Customizer

private _bottomPlaceholder: PlaceholderContent | undefined;
public onInit(): Promise<void> {
    Log.info(LOG_SOURCE, `Initialized ${strings.Title}`);
    // Added to handle possible changes on the existence of placeholders.
    this.context.placeholderProvider.changedEvent.add(this, this._renderPlaceHolders);
    // Call render method for generating the HTML elements.
    this._renderPlaceHolders();
    return Promise.resolve();
}

Implement _renderPlaceHolders method

private _renderPlaceHolders(): void {
    console.log('Available placeholders: ',
        this.context.placeholderProvider.placeholderNames.map(name => PlaceholderName[name]).join(', '));
    // Handling the bottom placeholder
    if (!this._bottomPlaceholder) {
        this._bottomPlaceholder =
            this.context.placeholderProvider.tryCreateContent(
                PlaceholderName.Bottom,
                { onDispose: this._onDispose });
        // The extension should not assume that the expected placeholder is available.
        if (!this._bottomPlaceholder) {
            console.error('The expected placeholder (Bottom) was not found.');
            return;
        }
    }
}

Use this.context.placeholderProvider.tryCreateContent to get access to the placeholder, without assuming that the placeholder will exist.

Implement the OnDispose method

private _onDispose(): void {
    console.log('[ReactHeaderFooterApplicationCustomizer._onDispose] Disposed custom top and bottom placeholders.');
}

Implement React component as footer

Add a new file to the solution – ReactFooter.tsx.

import * as React from "react";
import { Link } from 'office-ui-fabric-react/lib/Link';
import { CommandBar, ICommandBarItemProps } from 'office-ui-fabric-react/lib/CommandBar';
export interface IReactFooterProps {}
export default class ReactFooter extends React.Component<IReactFooterProps> {
    constructor(props: IReactFooterProps) {
        super(props);
    }
    public render(): JSX.Element {
        return (
            <div className={"ms-bgColor-themeDark ms-fontColor-white"}>
                <CommandBar
                    items={this.getItems()}
                />
            </div>
        );
    }
    // Data for CommandBar
    private getItems = (): ICommandBarItemProps[] => {
        return [
            {
                key: 'microsoft',
                name: 'Microsoft',
                cacheKey: 'myCacheKey', // changing this key will invalidate this items cache
                iconProps: {
                    iconName: 'AzureLogo'
                },
                href: 'https://www.Microsoft.com'
            },
            {
                key: 'officeUIFabric',
                name: 'Office UI Fabric',
                iconProps: {
                    iconName: 'OneDrive'
                },
                href: 'https://dev.office.com/fabric',
                ['data-automation-id']: 'uploadButton'
            }
        ];
    }
}

Open src\extensions\reactHeaderFooter\ReactHeaderFooterApplicationCustomizer.ts. Add below imports.

import * as React from "react";
import * as ReactDOM from "react-dom";
import ReactFooter, { IReactFooterProps } from "./ReactFooter";

Update _renderPlaceHolders method to include our React component.

private _renderPlaceHolders(): void {
    console.log('Available placeholders: ',
        this.context.placeholderProvider.placeholderNames.map(name => PlaceholderName[name]).join(', '));    
    // Handling the bottom placeholder
    if (!this._bottomPlaceholder) {
        this._bottomPlaceholder = this.context.placeholderProvider.tryCreateContent(
            PlaceholderName.Bottom,
            { onDispose: this._onDispose }
        );
        // The extension should not assume that the expected placeholder is available.
        if (!this._bottomPlaceholder) {
            console.error('The expected placeholder (Bottom) was not found.');
            return;
        }
        const elem: React.ReactElement<IReactFooterProps> = React.createElement(ReactFooter);
        ReactDOM.render(elem, this._bottomPlaceholder.domElement);
    }
}

Test the extension

Open serve.json under the config folder.

Update the properties section to include the page URL to test.

private _renderPlaceHolders(): void {
    console.log('Available placeholders: ',
        this.context.placeholderProvider.placeholderNames.map(name => PlaceholderName[name]).join(', ')); 
    // Handling the bottom placeholder
    if (!this._bottomPlaceholder) {
        this._bottomPlaceholder = this.context.placeholderProvider.tryCreateContent(
            PlaceholderName.Bottom,
            { onDispose: this._onDispose }
        );
        // The extension should not assume that the expected placeholder is available.
        if (!this._bottomPlaceholder) {
            console.error('The expected placeholder (Bottom) was not found.');
            return;
        }
        const elem: React.ReactElement<IReactFooterProps> = React.createElement(ReactFooter);
        ReactDOM.render(elem, this._bottomPlaceholder.domElement);
    }
}

On the command prompt, type the below command.

gulp serve

The SharePoint site will open. Click “Load debugs scripts”.

Observe the footer on the page.

Summary

Application customizer SharePoint Framework extension helps to extend the predefined placeholders on Modern SharePoint pages. React components help to develop functionality independently by maintaining the separation of concerns. These React components can be used as part of the application customizer.