Javascript Events, Capturing Works Bubbling Doesn't

My understanding of JS event propagation is that an event first 'captures' down the DOM tree, then 'bubbles' back up, triggering handlers along the way.

Solution 1:

dispatchEventdispatches your event. Summarizing, that means

When an event is dispatched to an object that participates in a tree (e.g. an element), it can reach event listeners on that object's ancestors too.

First all object's ancestorevent listeners whose capture variable is set to true are invoked, in tree order.

Second, object's own event listeners are invoked.

And finally, and only if event's bubbles attribute value is true, object's ancestorevent listeners are invoked again, but now in reverse tree order.

Therefore, if the bubbles attribute is not true, the event won't bubble.

You can set the bubbles attribute to true when you create the event with Event:

event = newEvent(type [, eventInitDict])

Returns a new event whose type attribute value is set to type. The optional eventInitDict argument allows for setting the bubbles and cancelable attributes via object members of the same name.

Solution 2:

To get the effect you want (show nothing yet, then 0,1,2,...) you need to follow a couple of the previous answers, plus set capturing on the textbox. (otherwise you'll see show nothing yet, 1, 2,...). First you need to set bubbling to true on your event - like this:

function update() {
    var e = new Event("update",{bubbles:true});
    textbox.dispatchEvent(e);
}

Then you need to capture the event (set to true) - like this:

// Event starts here
textbox = document.getElementById("textbox");
textbox.addEventListener("update", function(e) {
    textbox.innerHTML = val;
}, true);

So everything looks like this:

// Event starts here
textbox = document.getElementById("textbox");
textbox.addEventListener("update", function(e) {
    textbox.innerHTML = val;
}, true);

// Should bubble here
body = document.getElementsByTagName("body")[0];
body.addEventListener("update", function(e) {
    val++;
    console.log(val)
}, false);


functionupdate() {
    var e = newEvent("update",{bubbles:true});
    textbox.dispatchEvent(e);
}

setInterval(update, 1000);

Solution 3:

You need to pass { bubbles: true } as the second argument to new Event( ... ) for the Event to bubble, as per the documentation on MDN, because bubbles defaults to false.

Updated jsfiddle example

Solution 4:

If you use the old (unfortunately deprecated) way, it does bubble. See https://jsfiddle.net/py9vyr7h/1/

function update() {
    varevent = document.createEvent('CustomEvent');
    // Second param says to bubble the eventevent.initEvent('update', true, true);
    textbox.dispatchEvent(event);
}