Detect intermediate node with javascript bubbling/capturing

Question

I need to capture an anchor node with an image inside using event delegation.

document.addEventListener(
  'click',
  function(event) {
    console.log(event.target);
    return true;
  },
  false
);

<a href="#" class="link">
  <img src="http://placehold.it/100x100" alt="">
</a>

event.target is always img.

How can check if the click was made on a node with class .link?

UPDATE: to be clear here is an example with jQuery

When I use jQuery.on() there is a node in this property in callback fucntion, not img node. With pure JS I can determine initial target only.

Answer 1

You can check if an element has a class by calling:

element.classList.contains('link');

What you want right now is to do something when an <img> within an <a class="link"> is clicked. To determine if the clicked <img> has a parent <a class="link"> we must traverse up its parent tree and check.

This is very similar behavior as the jQuery example you have, i.e.

$('body').on('click', '.link', callback)

except the jQuery matches a whole query, not just a class.

Here's how you could do this:

// function to determine if the element has the link class
const hasLinkClass = element => element
  ? element.classList && element.classList.contains('link')
  : false;

// function that accepts an event handler and returns
// a wrapper function arround it.
// The wrapper is called it if the passed in event 
// object contains as its target an <img> with a parent
// with .link class
function filterImagesWithinLinks(handler) {
  return function(event) {
    let elem = event.target;

    // ignore clicks that are not on an image (it might be better to be more specific here)
    if (elem.tagName === 'IMG') {
    
      // filter until we find the parent with .link class
      while (elem && !hasLinkClass(elem)) {
        elem = elem.parentNode;
      }

      // if a parent with .link class was found, 
      // call the original handler and set its `this`
      // to the parent.
      if (elem) {
        handler.call(elem, event);
      }
    }
  };
}

// function handler that fires when 
// an <img> that has a parent with 
// class 'link' was clicked
function handler(event) {
  console.log('target : ', event.target);
  console.log('this   : ', this);
}

document.addEventListener(
  'click',
  filterImagesWithinLinks(handler),
  false
);

a.link {
  display: block;
  padding: 10px;
  background: #018bbc;
}

.middle {
  background: salmon;
  padding: 10px;
  text-align: center;
}

<a href="#" class="link">
  <p class="middle">
    <img src="http://placehold.it/100x100" alt="" />
  </p>
</a>

Answer 2

If you add some text or other content to the anchor tag, it will be easier to see the difference between the a and the img. See this example on JSFiddle -- it shows whether or not an element of the class link was clicked:

https://jsfiddle.net/Lppt4hyk/4/

Here's the code (only slightly modified from yours):

<a href="#" class="link"> Anchor
  <img src="http://placehold.it/100x100" alt="">
</a>

document.addEventListener(
  'click',
    function( event ) {
            var patt = /(?:^link | link$|^link$| link )/g;
            if (patt.test(event.target.className)) {
        alert('link class was clicked');
      }
      else { alert('link class was not clicked'); }
    return true;
  },
    false
);

div {
  background: red;
  display: block;
  height: 90%;
  width: 90%;
}

.n1 {
    background: yellow;
}

.n2 {
    background: green;
}

UPDATE: Added check for the link class name if it's not the only class assigned to that element.

UPDATE: Added regex checks to weed out link as part of a larger word.