Vanilla JS event delegation - dealing with child elements of the target element

Newer browsers

Newer browsers support .matches:

this.container.addEventListener('click', function(e){
    if (e.target.matches('#game-again,#game-again *')) {
        e.stopPropagation();
        self.publish('primo:evento');
    }
});

You can get the unprefixed version with

var matches = document.body.matchesSelector || document.body.webkitMatchesSelector || document.body.mozMatchesSelector || document.body.msMatchesSelector || document.body.webkitMatchesSelector

And then use .apply for more browsers (Still IE9+).

Older browsers

Assuming you have to support older browsers, you can walk up the DOM:

function hasInParents(el,id){
    if(el.id === id) return true; // the element
    if(el.parentNode) return hasInParents(el.parentNode,id); // a parent
    return false; // not the element nor its parents
}

However, this will climb the whole dom, and you want to stop at the delegation target:

function hasInParentsUntil(el,id,limit){
    if(el.id === id) return true; // the element
    if(el === limit) return false;
    if(element.parentNode) return hasInParents(el.parentNode,id); // a parent
    return false; // not the element nor its parents
}

Which, would make your code:

this.container.addEventListener('click', function(e){
    if (hasInParentsUntil(e.target,'game-again',container)) { // container should be 
        e.stopPropagation();                                  // available for this
        self.publish('primo:evento');
    }
});

Alternate Solution:

MDN: Pointer events

Add a class to all nested child elements (.pointer-none)

.pointer-none {
  pointer-events: none;
}

Your mark-up becomes

<div id="quiz">
    <button id="game-again" class="game-again">
        <span class="icon-spinner icon pointer-none"></span>
        <span class="pointer-none">Go again</span>
    </button>
</div>

With the pointer set to none, the click event wouldn't fire on those elements.

https://css-tricks.com/slightly-careful-sub-elements-clickable-things/