Why does `this` behave unexpectedly when using arrow functions in event handlers?

JavaScript - Arrow Functions and Event Handlers

When using arrow functions as callbacks for event handlers, the value of this within the function is unexpected. This blog post explains the reason behind this behavior and provides a solution to access the intended element using event.currentTarget.

Arrow Functions and Lexical Scope

Unlike regular functions, arrow functions do not have their own context or scope for this. Instead, they inherit the lexical scope of their surrounding context. In the example provided, the arrow function is defined within the click event handler of dom.videoLinks. Therefore, this within the arrow function refers to the dom.videoLinks element.

Event Listeners and event.currentTarget

Event listeners are attached to specific elements and are executed when certain events occur. When an event is triggered, the event object contains information about the target element that triggered the event and the current target element that has the event listener attached to it.

The event.target property refers to the element that directly triggered the event. In most cases, this is the element that was clicked, hovered over, or received focus.

The event.currentTarget property, on the other hand, refers to the element that has the event listener attached to it. This is the element that the event is being processed on at the time of execution.

Using event.currentTarget in Arrow Functions

To access the intended element within an arrow function event handler, use event.currentTarget instead of this. Here's a modified version of the code:

<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

In general, event.currentTarget should be used over event.target when working with event handlers. This is because events can bubble up or capture down the DOM tree, and using event.target may not always refer to the element you intend to target.

event.currentTarget consistently refers to the element that has the event listener attached to it, regardless of the event flow.

Conclusion

When using arrow functions in event handlers, remember to use event.currentTarget to access the intended element. Keep in mind the distinction between event.target and event.currentTarget when working with event bubbling and capturing to ensure accurate event handling.

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