Officejs

Office.js is the JavaScript API used by Office Add-ins to extend Microsoft Office applications. It enables developers to write cross-platform web-based code that runs inside Word, Excel, PowerPoint, and Outlook, providing access to documents, mail items, and the user interface. Add-ins are delivered with a manifest and can appear as task panes, content add-ins, or mailbox apps.

The API is exposed through the Office.js library, loaded by the add-in and accessed via the global Office object. Developers initialize with Office.onReady and use host-specific APIs, such as Excel.run with the Excel JavaScript API, Word APIs, or Outlook APIs. Most operations are asynchronous and batched, completed with context.sync to apply changes to the host document or item.

The API surface uses requirement sets to denote capabilities across hosts, enabling use of newer features while preserving compatibility. Common capabilities include reading and writing content, formatting ranges, working with shapes and content controls, and responding to user interactions through task panes, dialogs, and ribbon commands. The model also supports event handling and custom functions in Excel.

Deployment and compatibility: Office Add-ins built with Office.js run in Office on Windows and macOS, Office for the web, and many mobile clients, depending on host support. Add-ins are packaged with an XML manifest and distributed via the Office Store or centralized deployment by IT administrators. Microsoft provides documentation, samples, and migration guidance.