Emulate jQuery "on" with selector in pure Javascript

Question

I would emulate in pure Javascript the main functionality of jQuery .on( events , selector , data) method.

For example

$(document).on('click','.button',function() {
   console.log("jquery onclick"); 
});

I thought it was enough make something like this

document.addEventListener('click',function(e) {
    if(e.target.className == 'button2') {
         console.log("It works");   
    }
});

However when I have this html structure:

<button class="button2">Hello <span>World</span></button>

my script doesn't works when the click event is triggered on span element, because e.target is span. (I ignore for this question the complexity of elements with multiple class, and crossbrowsers compatibility)

The source of jQuery is not simple to read and I don't understand how it works (because the first piece of code, in jQuery, works with my html structure).

I need this method because my html is dynamic, and buttons with this class are created, deleted and re-created many times. I don't want add listeners every times.

I would avoid, if possible, to include jquery library.

So, I can do this?

Here the jsFiddle for testing.

Answer 1

Update for 2017: current DOM standards like closest mean this is now much easier.

const addEventForChild = function(parent, eventName, childSelector, cb){      
  parent.addEventListener(eventName, function(event){
    const clickedElement = event.target,
    matchingChild = clickedElement.closest(childSelector)
    if (matchingChild) cb(matchingChild)
  })
};

To use it just:

addEventForChild(parent, 'click', '.child', function(childElement){
  console.log('Woo click!', childElement)
})

Here's a jsfiddle

Answer 2

This is actually surprisingly simple. You're on the right track, but it's not quite there.

Here's the functions I use:

window.addEvent = function(elem,type,callback) {
    var evt = function(e) {
        e = e || window.event;
        return callback.call(elem,e);
    }, cb = function(e) {return evt(e);};
    if( elem.addEventListener) {
        elem.addEventListener(type,cb,false);
    }
    else if( elem.attachEvent) {
        elem.attachEvent("on"+type,cb);
    }
    return elem;
};
window.findParent = function(child,filter,root) {
    do {
        if( filter(child)) return child;
        if( root && child == root) return false;
    } while(child = child.parentNode);
    return false;
};
window.hasClass = function(elem,cls) {
    if( !('className' in elem)) return;
    return !!elem.className.match(new RegExp("\\b"+cls+"\\b"));
};

The window.findParent is central to the whole thing, as you can see when I show you how to attach your desired on listener:

window.addEvent(document.body,"click",function(e) {
    var s = window.findParent(e.srcElement || e.target,function(elm) {
        return window.hasClass(elm,"button");
    },this);
    if( s) {
        console.log("It works!");
    }
});

Answer 3

Easy and short code:

function onEvt(type, callback) {
    if (document.attachEvent) {
        document.attachEvent("on" + type, function (e) {
            callback(e.target);
        });
    } else {
        document.addEventListener(type, function (e) {
            callback(e.target);
        }, false);
    }
}

Call the function like this:

onEvt('click', function(elem){ // click, mouseover etc...
    // for class
    if(elem.classList.contains('classname')){
        // do stuff
    }
    // for attribute
    if(elem.hasAttribute('target')){
        // do stuff
    }
});

Answer 4

You can use function Marchy8 on github via link or extend it by doing the following.

Firstly create $() selector function:

function $(selector) {
    return selector;
}

HTMLElement = typeof (HTMLElement) != "undefined" ? HTMLElement : Element;
String.prototype.on = function(type, callback){
    var selector = this;
    document.body.addEventListener(type, function (event) {
        if (event.target.matches(selector)) {
            callback.call(event.target);
        }
    });
}

$(".test").on("click", function(e) {
    console.log(this.innerHTML);
    this.style.color = "red";
});

<div class="test">Click Here</div>
<div class="test">Click Here-1</div>