function addSimultaneousEventListeners(eventNames, callback, options) {
    const defaultOptions = {
        inOrder: true,  // the events should be fired in the order specified in eventNames array or not
        tolerance: 500, // the tolerance time between the first and the last event in milliseconds,
                        // you can rarely fire two events at the exact moment
    }
    // merge default options with user options
    const mergedOptions = {
        ...defaultOptions,
        ...options
    };
    const inOrder = mergedOptions.inOrder;
    const tolerance = mergedOptions.tolerance;

    eventNames = Object.freeze(eventNames); // make array immutable
    let eventList = [];
    eventNames.forEach((eventName) => {
        document.addEventListener(eventName, listener);
    })

    function listener(e) {
        eventList.push(e);
        // trim eventList size
        if (eventList.length > eventNames.length) {
            eventList = eventList.slice(eventList.length - eventNames.length);
        }
        // console.log("eventList: " + eventList.reduce((string, event) => {
        //     return string + event.type + "@" + Math.round(event.timeStamp) + ", ";
        // }, ""));
        const eventStack = eventNames.slice(); // copy array
        if (eventList.length === eventNames.length) {
            const firstEvent = eventList[0];
            for (let i = 0; i < eventList.length; i++) {
                const currentEvent = eventList[i];
                let currentEventName;
                if (inOrder) {
                    currentEventName = eventNames[i];
                } else {
                    const eventIndex = eventStack.indexOf(currentEvent.type);
                    if (eventIndex >= 0) {
                        currentEventName = currentEvent.type;
                        eventStack.splice(eventIndex, 1);
                    } else {
                        return; // not the right events fired
                    }
                }
                if (currentEvent.type !== currentEventName || !approximatelyEqual(firstEvent.timeStamp, currentEvent.timeStamp)) {
                    return; // not the right event type or both events are NOT fired at the same time
                }
            }
            // eventList will be in order when inOrder is true
            // otherwise it will be the order the user fired them
            // you should always test for event types
            callback(eventList);
        }
    }

    // test if a and b are equal within the tolerance range
    function approximatelyEqual(a, b) {
        return (Math.abs(a - b) <= tolerance);
    }
}
// Demo: detect keydown, click, and contextmenu fire at about the same time in that order
addSimultaneousEventListeners(["keydown", "click", "contextmenu"], // events registered
(eventList) => { // listener
    console.log("you pressed a key, left clicked, and right clicked the document!");
    console.log("eventList: ", eventList);
},
{ // options
    inOrder: true
});