如何模拟触发touchstart事件

window.onload = function () {
 
    var bot = document.getElementById('bot');
    bot.addEventListener('touchstart', function () {
        alert('touchstart');
    });
     
    creatTouchstartEventAndDispatch(bot);
     
    function creatTouchstartEventAndDispatch (el) {
        var event = document.createEvent('Events');
        event.initEvent('touchstart', true, true);
        el.dispatchEvent(event);
    }
     
}