trigger event javascript

//Listen for the event
window.addEventListener("MyEventType", function(evt) {
    alert(evt.detail);
}, false);

//Dispatch an event
var evt = new CustomEvent("MyEventType", {detail: "Any Object Here"});
window.dispatchEvent(evt);

// Simple trigger event
document.querySelector(theElem).dispatchEvent(new Event('mouseover'))

var event = new CustomEvent("song_started", { "detail": "Britney is singing baby!"});
document.dispatchEvent(event); //Trigger/Dispatch the event

//Lets listen for event (do this before you dispatch)
document.addEventListener("song_started", function(e) {
    console.log(e.detail);// "Britney is singing baby!"
});