simulate-event.js

function simulate(element, eventName, options) {
    var opt = {
        pointerX: 0,
        pointerY: 0,
        button: 0,
        ctrlKey: false,
        altKey: false,
        shiftKey: false,
        metaKey: false,
        bubbles: true,
        cancelable: true
    }
    Object.assign(opt, options)

    var oEvent
    switch (eventName) {
        case "unload":
        case "abort":
        case "error":
        case "select":
        case "change":
        case "submit":
        case "reset":
        case "focus":
        case "blur":
        case "resize":
        case "scroll":
            oEvent = document.createEvent("HTMLEvents")
            oEvent.initEvent(eventName, opt.bubbles, opt.cancelable)
            break

        case "click":
        case "dblclick":
        case "mousedown":
        case "mouseup":
        case "mouseover":
        case "mousemove":
        case "mouseout":
        case "keydown":
        case "keyup":
            oEvent = document.createEvent("MouseEvents")
            oEvent.initMouseEvent(eventName, opt.bubbles, opt.cancelable, document.defaultView,
                opt.button, opt.pointerX, opt.pointerY, opt.pointerX, opt.pointerY,
                opt.ctrlKey, opt.altKey, opt.shiftKey, opt.metaKey, opt.button, element)
            break

        default:
            throw new SyntaxError('Only HTMLEvents and MouseEvents interfaces are supported')
    }

    element.dispatchEvent(oEvent)
}


/* https://stackoverflow.com/a/51893135/226844
*/
function simulateClick(elementToClick) {
    var simulateMouseEvent = function(element, eventName, coordX, coordY) {
      element.dispatchEvent(new MouseEvent(eventName, {
        view: window,
        bubbles: true,
        cancelable: true,
        clientX: coordX,
        clientY: coordY,
        button: 0
      }));
    };

    var box = elementToClick.getBoundingClientRect(),
        coordX = box.left + (box.right - box.left) / 2,
        coordY = box.top + (box.bottom - box.top) / 2;

    simulateMouseEvent (elementToClick, "mousedown", coordX, coordY);
    simulateMouseEvent (elementToClick, "mouseup", coordX, coordY);
    simulateMouseEvent (elementToClick, "click", coordX, coordY);
}

Source: https://stackoverflow.com/a/6158050/226844