This is a simple web application that uses the browser Gamepad API and roslibjs to publish gamepad (joystick / game controller) input to ROS via a rosbridge, without installing anything.
As an alternative, you might want to use the joy package.
Navigate to https://whoigit.github.io/ros-web-gamepad/?rosbridge-websocket-url=ws://127.0.0.1:9090 (insert the correct address for your rosbridge), connect a gamepad to your computer, and press any gamepad button.
Your browser's security settings may prevent the page from connecting to the rosbridge. In this case, download the HTML file and open it locally.
The application publishes sensor_msgs/Joy messages to the /joy topic at 10 Hz.
Most browsers support the Gamepad API, but Safari's support seems buggy. At the time of writing, Chrome works well.
This has been tested against ROS Melodic. It probably does not work with ROS2.
The appearance of the gamepad indicators is derived from ipywidgets.