In SpFx we have extensions as similar to webparts, library. In short, extensions are more like injects scripts to our SharePoint page. In our previous session, we discussed about the library in SPFX. https://tejasadventure.blogspot.com/2021/07/spfx-create-custom-library.html Create a demo now: Create a scaffold. Select the client side component - choose "extension". Application customizer: 1. which client side extension do you want to create - choose "Application customizer". 2. open in VS code. 3. We can see boiler plate code. 4. Under manifeast.json file we can obser "componentType" as "Extension", "extensionType" as "ApplicationCustomizer", 5. In .ts file, We can see interface has one property called textMessage: string. Now go to the config folder, you can see serve.json Using serve.json file, we can Inject the code to our SharePoint page. In serve.json, we can find property called textMessage, It has value as well....