dist/event-target-shim.js
function EventTarget() {
    /*eslint-disable consistent-return */
    if (this instanceof EventTarget) {
        listenersMap.set(this, new Map());
        return
    }
    if (arguments.length === 1 && Array.isArray(arguments[0])) {
        return defineCustomEventTarget(arguments[0])
    }
    if (arguments.length > 0) {
        const types = new Array(arguments.length);
        for (let i = 0; i < arguments.length; ++i) {
            types[i] = arguments[i];
        }
        return defineCustomEventTarget(types)
    }
    throw new TypeError("Cannot call a class as a function")
    /*eslint-enable consistent-return */
}
function EventTarget() {
    /*eslint-disable consistent-return */
    if (this instanceof EventTarget) {
        listenersMap.set(this, new Map());
        return
    }
    if (arguments.length === 1 && Array.isArray(arguments[0])) {
        return defineCustomEventTarget(arguments[0])
    }
    if (arguments.length > 0) {
        const types = new Array(arguments.length);
        for (let i = 0; i < arguments.length; ++i) {
            types[i] = arguments[i];
        }
        return defineCustomEventTarget(types)
    }
    throw new TypeError("Cannot call a class as a function")
    /*eslint-enable consistent-return */
}
EventTarget.

- This is constructor if no arguments.
- This is a function which returns a CustomEventTarget constructor if there are arguments.

For example:

class A extends EventTarget {}
class B extends EventTarget("message") {}
class C extends EventTarget("message", "error") {}
class D extends EventTarget(["message", "error"]) {}