Explain onClickCapture in JavaScript

How can I invoke a function if a child element is clicked.

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3 min read

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Introduction

  • Explanation of what onClickCapture is and how it differs from the onClick property

  • A brief overview of event propagation in the DOM

Background

A quick refresher on event phases of JavaScript on a browser

There are 3 phases in the lifecycle of an event in JavaScript

  1. Capturing Phase

  2. Target Phase

  3. Bubbling Phase

This what it is looks like on a high level -

But for the scope of this post, we are interested in the capturing phase.

Capturing Phase

An event is in capturing phase when the event goes down to the target element.

As you can see from the above image the Button is the target element, so that event will start flowing from the top that is HTML till the Button.

How the onClickCapture function fits into the capturing phase

If you notice in the above image, I have declared a function onClickCapture on DIV which is the parent of Button

So, as per the theory **onClickCapture** should invoke a function (if any) associated with it while in the capturing phase.

That also means, **onClickCapture** on DIV will execute before onClick event of Button.

Here is a CodePen for you to demonstrate the event:

https://codepen.io/sagars_01/pen/oNMZKyY

When it makes sense to use onClickCapture

As front-end engineers most of the time, we tend to use reusable components and most of the time we don’t have any control over the code of the component.

For example, at Lowe’s, we have huge teams which work across different products and we share React Components all the time.

Situation

Imagine yourself in a similar situation where you’re using a button(B1) built by another team and B1 has an onClick method that has an event.stopPropagation(). Your use case is to trigger an API call from your codebase whenever the button(B1) has been clicked.

Note: event.stopPropagation() will stop the event from bubbling.

Solution

In this situation, you can use onClickCapture on the parent div or tag of the button (B1) to achieve your result.

Example here in JSFiddle

https://jsfiddle.net/sagars71/hzev6um7/

Conclusion

The key takeaways for you are:

  1. There are 3 phases of an event in JavaScript.

  2. onClickCapture works on the Event Capturing Phase

  3. onClickCapture can be used when you want to know if a child element has been clicked.

I encourage you to play with the JSFiddle and try to fit your use case on the same.

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