addEventListener on NodeList

Question

Does NodeList support addEventListener. If not what is the best way to add EventListener to all the nodes of the NodeList. Currently I am using the code snippet as show below, is there a better way to do this.

var ar_coins = document.getElementsByClassName('coins');
for(var xx=0;xx < ar_coins.length;xx++)
{
        ar_coins.item(xx).addEventListener('dragstart',handleDragStart,false);
}

Answer 1

There is no way to do it without looping through every element. You could, of course, write a function to do it for you.

function addEventListenerList(list, event, fn) {
    for (var i = 0, len = list.length; i < len; i++) {
        list[i].addEventListener(event, fn, false);
    }
}

var ar_coins = document.getElementsByClassName('coins');
addEventListenerList(ar_coins, 'dragstart', handleDragStart); 

or a more specialized version:

function addEventListenerByClass(className, event, fn) {
    var list = document.getElementsByClassName(className);
    for (var i = 0, len = list.length; i < len; i++) {
        list[i].addEventListener(event, fn, false);
    }
}

addEventListenerByClass('coins', 'dragstart', handleDragStart); 

And, though you didn't ask about jQuery, this is the kind of stuff that jQuery is particularly good at:

$('.coins').on('dragstart', handleDragStart);

Answer 2

The best I could come up with was this:

const $coins = document.querySelectorAll('.coins')
$coins.forEach($coin => $coin.addEventListener('dragstart', handleDragStart));

Note that this uses ES6 features, so please make sure to transpile it first!

Answer 3

There actually is a way to do this without a loop:

[].forEach.call(nodeList,function(e){e.addEventListener('click',callback,false)})

And this way is used in one of my one-liner helper libraries - nanoQuery.

Answer 4

The simplest example is to add this functionality to NodeList

NodeList.prototype.addEventListener = function (event_name, callback, useCapture)
{
    for (var i = 0; i < this.length; i++)
    {
      this[i].addEventListener(event_name, callback, useCapture);
    }
};

Now you can do:

document.querySelectorAll(".my-button").addEventListener("click", function ()
{
    alert("Hi");
});

In the same way, you can do a forEach loop

NodeList.prototype.forEach = function (callback)
{
    for (var i = 0; i < this.length; i++)
    {
      callback(this[i], i);
    }
};

Using:

document.querySelectorAll(".buttons").forEach(function (element, id)
{
    input.addEventListener("change", function ()
    {
        alert("button: " + id);
    });
});

EDIT : note that NodeList.prototype.forEach has existed ever since november 2016 in FF. No IE support though

Answer 5

in es6, you can do a array from nodelist, using Array.from, e.g.

ar_coins = document.getElementsByClassName('coins');
Array
 .from(ar_coins)
 .forEach(addEvent)

function addEvent(element) {
  element.addEventListener('click', callback)
}

or just use arrow functions

Array
  .from(ar_coins)
  .forEach(element => element.addEventListener('click', callback))

Answer 6

Another solution is to use event delegation. You just use addEventListener to the closest parent of the .coins elements and use event.target in the callback to check if the click was really on an element with the class "coins".

Answer 7

I suppose another option would be to define addEventListener on NodeList using Object.defineProperty. That way you can treat the NodeList as you would a single Node.

As an example, I created a jsfiddle here: http://jsfiddle.net/2LQbe/

The key point is this:

Object.defineProperty(NodeList.prototype, "addEventListener", {
    value: function (event, callback, useCapture) {
        useCapture = ( !! useCapture) | false;
        for (var i = 0; i < this.length; ++i) {
            if (this[i] instanceof Node) {
                this[i].addEventListener(event, callback, useCapture);
            }
        }
        return this;
    }
});

Answer 8

You could also use prototyping

NodeList.prototype.addEventListener = function (type, callback) {
    this.forEach(function (node) {
        node.addEventListener(type, callback);
    });
};