The Gamepad.id property of the Gamepad interface returns a string containing some information about the controller.
The exact syntax is not strictly specified, but in Firefox it will contain three pieces of information separated by dashes (-):
For example, a PS2 controller returned 810-3-USB Gamepad.
This information is intended to allow you to find a mapping for the controls on the device as well as display useful feedback to the user.
A string primitive.
window.addEventListener("gamepadconnected", () => {
const gp = navigator.getGamepads()[0];
gamepadInfo.textContent = `Gamepad connected at index ${gp.index}: ${gp.id}.`;
});