Is it possible to create custom widgets in ArcGIS Online?

Answer

Some occasions call for creating custom widgets in ArcGIS Online, however, ArcGIS Online does not support custom widgets. As a workaround, use ArcGIS Web AppBuilder (Developer Edition) or ArcGIS Experience Builder (Developer Edition) to create the custom widgets and deploy the application or experience in ArcGIS Online. To do so, follow the instructions described below:

In ArcGIS Web AppBuilder (Developer Edition)

1. Create custom widgets using ArcGIS Web AppBuilder (Developer Edition). Follow the steps outlined in ArcGIS Web AppBuilder: Create a custom in-panel widget.
2. Host the application with the custom widgets on the organization's web server. Refer to ArcGIS Web AppBuilder: Deploy the app for steps to do this.
3. Add the application as an item in ArcGIS Online. Refer to ArcGIS Online: Items in ArcGIS Online for steps to do this.

In ArcGIS Experience Builder (Developer Edition)

1. Create custom widgets using ArcGIS Experience Builder (Developer Edition). Refer to ArcGIS Experience Builder: Create a starter widget for instructions and ArcGIS Experience Builder: Getting started with widget development for more information.
2. Host the experience with the custom widgets on the organization’s web server. Refer to ArcGIS Experience Builder: Deploy the experience for steps to do this.
3. Add the experience as an item in ArcGIS Online. Refer to ArcGIS Online: Items in ArcGIS Online for instructions.

Note:
Custom widgets can be shared publicly. For more information, refer to ArcGIS Online: Share items with everyone.