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Gabe for AMP Agency

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Quick and Easy JS Parallax Effect

I was recently tasked with creating a micro-site for one of our clients at work. This particular client wanted a small site that would showcase their new line of chips and dip. This being my first client deliverable at AMP, I was pretty excited to get started and show my team that I'm more than just a pretty face.

So I meet with my project manager and we go over the designs and discuss the functionality that the page would have behind its different sections. It was pretty straight forward, a hero, a featured products grid, a store locator, a product carousel and a footer. The only thing is the hero would feature a parallax effect where some chips would pop out and move up the page as the user scrolls down. While this was going to take a bit of work, a major bonus for me was that most of the other pieces of the site were already built for me thanks to my co-worker Ethan who is a pro at cranking out these microsites for our clients. So I pull down his github repository and setup my local, we're using Zurb's Foundation framework for this client. I start putting together the pieces and building out the page according to the designer's comp. After about 3 - 4 hours I finish what I consider the base of the page. I have all the sections in place and all the components are functioning as expected. It was time to get to the parallax effect.

9 lines of JavaScript

No bullshit. After hours of playing around with different parallax libraries to try and create the effect I wanted, my boss casually slides over in his chair and says "That looks fun. Send this to me, let me give it a shot". So I do. 15 minutes later he sends me over a JavaScript file and tells me that it's all set. I copy his code into my JavaScript file, compile it and open it up in FireFox to test it. It worked. It worked beautifully. I was so amazed, I kept scrolling back and forth making the chips move for what felt like hours. See the code below.

Pretty Cool. And wicked simple too. Granted with this version you need jQuery in order for it to run, but creating the same result in vanilla js is possible.

Discussion (6)

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rikschennink profile image
Rik Schennink

Awesome!

Some performance improvements you could make. Don't adjust marginTop, it will cause a reflow (which means the browser has to recalculate all element positions), instead, update transform as that can be applied by the GPU, is hardware accelerated, and does not cause a reflow.

You can also request the scroll offset once and then loop over the elements. Requesting scroll offset will result in another reflow as the browser will have to calculate the offset to be sure it's returning the right value. Because you alter the marginTop the layout has changed and it will have to do this for each chip.

Marking the event listener as passive will result in another slight performance improvement, this tells the browser the event won't be cancelled.

The final thing todo is to only update the view when the browser draws to the screen. The prevents multiple calls to the function when only one of the calls is drawn.

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gabe profile image
Gabe Author

This is awesome, and exactly the kind of feedback i was looking for when I originally posted this! Thank you! I’ll be giving your code a shot later today when I get into work.

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rikschennink profile image
Rik Schennink

Wonderful! Glad to hear it's of use to you!

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jon profile image
Jon Bishop

I missed that passive event listener adoption. So useful.

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jdmedlock profile image
Jim Medlock

Cool! Thanks for this gem.

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gabe profile image
Gabe Author

Happy to help!