How does `this` behave in arrow functions used as event handlers in JavaScript?

Javascript - arrow functions this in event handler

In ES6, there's a new concept of arrow functions that offer a concise and cleaner way to define functions. However, when using arrow functions as callbacks in event handlers, understanding the behavior of this becomes crucial.

The Problem

In the provided code, an event.currentTarget property is not used, and the arrow function returns undefined when clicking on elements.

this in Arrow Functions

Unlike regular functions, the value of this inside an arrow function is determined by where the arrow function is defined, not where it is used. In the provided example, the arrow function is defined in the context of a larger function, which can lead to unexpected behavior.

The Solution

To address this issue, instead of accessing this, event.currentTarget should be used to get the element to which the handler is bound. event.currentTarget always refers to the DOM element whose EventListeners are currently being processed. Here's how the code can be modified:

<code class="javascript">dom.videoLinks.click((e) => {
  e.preventDefault();
  console.log(e.currentTarget);
  var self = e.currentTarget,
    url = self.attr(configuration.attribute);

  eventHandlers.showVideo(url);

  // Deactivate any active video thumbs
  dom.videoLinks.filter('.video-selected').removeClass('video-selected');

  // Activate selected video thumb
  self.addClass('video-selected');
});</code>

.currentTarget vs .target

Another important difference to note is the behavior of event.currentTarget and event.target in the context of event bubbling and capturing.

• currentTarget: Represents the element that has the event listener attached to it.
• target: Represents the element that triggered the event.

When dealing with nested elements and event propagation, using event.currentTarget ensures that the correct element is always referenced.

Example

The provided snippet demonstrates the difference between this, event.currentTarget, and event.target. By clicking on different elements, the output shows how the value of each property changes based on the element triggered and the context of the event listener.

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