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3rd Party JavaScript Packages


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Welcome to the fabulous day 4! Where we're already creating JavaScript modules... a fancy term that means we're writing import statements and export statements. And we're pulling this off entirely without a build system. Time for a happy dance!

But what about third-party packages? Head over to and search for a very important package called js-confetti. This package is all about celebrating, which... is exactly what we're doing during these 30 days! In the README, it says to use Yarn to install it. We are not going to do that. Instead, skip right down to the usage example. Copy that, head over to our app.js... and paste that in:

15 lines | assets/app.js
// ... lines 1 - 8
import JSConfetti from 'js-confetti';
const jsConfetti = new JSConfetti();
// ... lines 13 - 15

Side note: import statements always go at the top of your file. If you don't do that - if you do something weird like this, well, you can, but your browser will move this up to the top when it executes the code anyway. So we'll avoid being troublemakers.

Missing JavaScript Module Error

Ok: is this going to work? I mean... probably not because we haven't installed anything. But let's live recklessly and try it anyway! Error! A very important error:

Failed to resolve module specifier js-confetti. Relative references must start with either /, ./ or ../.

So what this is saying is that your browser found an import statement... and has no idea how to load that file. If an import statement starts with ./ or ../, your browser knows how to handle that: it looks for a file relative to this file. Easy peasy.

But if there is no ./ or ../, it's called a bare module. In that case, your browser looks for a match in the importmap. Right now, our importmap looks like it did before. Notably, we do not have a js-confetti key. And that's why we get this error.

This is one of the most important errors you'll see when coding with modules. And it'll look a bit different based on which browser you're using. Firefox, for example, phrases this error differently.

But regardless of the wording, this error almost always means the same thing: you're trying to use a third party package, but it's not installed.

Installing Packages with importmap:require

How do we install it? Glad you asked! Copy the package name, spin over and run:

php bin/console importmap:require js-confetti

That's it! Spin back over and... celebration! It works! Mad refreshing!

How does that work? Karma? Well, not surprisingly, if you view the page source, we have a new entry inside our importmap with a js-confetti key. And it points to a file in an assets/vendor/ directory. Interesting.

When we ran that command, it really did just one thing. It updated our importmap.php file. It added this entry right here:

25 lines | importmap.php
// ... lines 1 - 15
return [
// ... lines 17 - 20
'js-confetti' => [
'version' => '0.11.0',

Behind the scenes, it went out and found what the latest version was and put that here. And because we have a js-confetti item in importmap.php, it means that we're going to have a matching js-confetti key inside of the importmap on the page.

The assets/vendor/ Directory

Where does that file actually live? Up here in a new assets/vendor/ directory. If you dig, here is the actual file that's being loaded.

Two juicy details about this vendor/ directory. The first is: it's ignored from Git: you can see /assets/vendor/:

16 lines | .gitignore
// ... lines 1 - 11
###> symfony/asset-mapper ###
// ... line 13

Just like the composer vendor/ directory, this is not something that you should commit to your repository.

The second is more of a question: how do I get these files if I clone or update a project and some or all of the files are missing?

To find out, get crazy and destroy that directory. Muwahahaha. And now, to increase our reckless streak, try to refresh the page. Error! Awesome error!

The js-confetti vendor asset is missing: try running the importmap:install command.

Lovely idea! Spin over and try that:

php bin/console importmap:install

Just like composer install, that downloads whatever you need into assets/vendor/... and now it just works.

That's it! By day 4, we've already solved 3rd party packages! We don't even need a giant node_modules/ directory! I'm going to have to find some other way to fill my hard drive. Maybe, more Docker containers?

Ok, for tomorrow's adventure, we'll jazz up our site with some CSS. Stay tuned!