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Webpack Encore: Tips, Tricks, Questions & Best Practices

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SymfonyCon 2018 Presentation by Ryan Weaver

With Webpack, your JavaScript & CSS code can have superpowers you've only dreamed up. And with Symfony's Webpack Encore, you can get all of this with almost zero setup time!

In this talk, we'll quickly learn the basics of Webpack Encore, then, turn to the lessons we've learned over the past year: answer popular questions and explore common problems people run into when moving to Encore. We'll also dive into a host of lesser-known best practices that you can follow to make sure your frontend coding is as streamlined as possible. A modern frontend build system: all in the time of one talk!

How many people have seen the SymfonyCasts videos? I was going to explain that this is really my voice and the miracles of editing. It's really incredible what we can with that audio. Okay. I am Ryan. Hello nice to meet you. I'm the the lead of the documentation team. Also, a writer for KnpUniversity... wait SymfonyCasts.

Hey Ryan!

Changing a domain is harder than you think. I'm basically, if you've been around Symfony for a while, you probably know me, I'm a Symfony evangelist / fanboy. The husband of the much more talented and much more popular at the Symfony conferences, Leanna. How many people have met Leanna? Okay, yeah, okay. That's so great, because that means, there's many of you have such a great opportunity today to meet Leanna, give her a jumping high-five, like this style.

Leanna, can you raise your hand, just so everyone sees, right here? Yeah, so Leanna's right here, and you can find her afterwards. She's going to come up afterwards and wait for her high-fives. And the father to my much more handsome, charming son Beckett. So now, I have a kid, so now I get to show you pictures of my kid in the beginning. Whether you want to or not, so that's my son, Beckett.

Webpack: Totally New Way or Frontend Dev

Okay, so let's talk about Webpack and Encore. We are going to do just a little bit of explanation in the beginning, then talk about some lessons that we've learned over the past year and a half. And also, some new features, because a new version of Encore came out, only one month ago, and there are actually some really exciting changes that we've made in that version.

Okay so first of all, Webpack itself. What is Webpack? It's a very simple concept, it allows you to package all of your JavaScript and all of your CSS into one file each. And it works via require statements, so you can have one file app.js, require some other files, sort of like we used to do in PHP, require some other files, and that's it. It's just going to turn all of those into one app.js, and one app.css file. That's kind of cool.

Or we can explain Webpack as a totally new way of programming. This is actually what makes it hard. You have to completely unlearn everything you've learned about doing frontend programming. Because we've spent 15 years learning how to program in JavaScript with global variables. That's insane.

How many of you regularly use global variables in PHP? There's one brave hand. No, we don't program that way. How many of you do it in JavaScript? Everyone that does JavaScript, right? Because it wasn't possible before. You have to unlearn that. We basically have to retrain ourselves to program in JavaScript the same way that we program in PHP. Once you do it, it's an amazing experience.

Encore Basics

So, Encore is just a wrapper around Webpack. It's actually a Webpack configuration generator. It's a Node library, but we recommend installing it via a Composer package. I'll explain why later. There is a little bit of PHP in Encore, but it's mostly Node. Of course, it has a nice recipe when you install it: composer require encore.

Oh, actually see, things changed. That's slightly out of date because we should not have the ––dev there anymore. I'll explain why later. There is a small bit of code that you do want to run at run-time now.

composer require encore, okay, it downloads a few things. This is what it gives you. It gives you a package.json: that's the composer file basically for Node. Two files: a CSS file and a JavaScript file just to get you started. And that's basically it.

So, here is what the package.json looks like. It just requires two packages: Encore and the webpack-notifier is just cool because it makes cool desktop notifications when your build finishes. It's like ding, your build is done! It just makes it more fun. That's it.

The webpack.config.js file is where you configure Encore, how you tell Encore what you need. What you need is actually very simple. You just need to tell it where you want the output path, where you are going to put the final build files, and then you are going to point it, it's called an entry, you are going to point it to a single JavaScript file.

I'm saying go read that ./assets/js/app.js file. The first key app? That could be anything: that will ultimately control the name of your output file. If that first key, that first argument was foo, we would end up with a foo.js file.

But we're pointing it at app.js. What does app.js look like? Okay, here's a simple example. We can requires some JavaScript files, or we can even require CSS files. That's what we have here: we're actually requiring CSS from JavaScript. I'm going to talk about that in a little bit: that's very, very important. Then we actually need to install our dependencies. I really should have taken a screenshot of ... This is basically me running yarn install. Yarn is, there are two package managers in Node. Yarn is one of them. This is basically me running yarn install.

For some reason, yarn lets you be so incredibly lazy that you can just say, yarn and it installs for you. This is me running yarn install and the end result is... boom! We end up with tons of files in a node_modules/ directory, which is the vendor/ directory. At this point, we have basically just required two packages from Node, and installed them. That's it.

To actually run Encore, you're going to run yarn encore dev. There is also a yarn encore production you'll see later: that's the mode that minifies all of your files and does other optimizations. Of course, there is a --watch so you don't have to run every time. Every time you modify file, this is going to re-output your files.

The end result of this is that you get two files. Actually, you guys are probably good at counting, you get four files. The only important ones yet are the app.js and app.css. What happened was: we told the Webpack to look at our app.js file. It follows all of the require statements: all the JavaScript we required, all of the CSS we required, and got all of that JavaScript and CSS, and it finally writes one app.js, and one app.css file. Then we just need to include those in our template, completely like normal.

In some ways, I want this to seem very underwhelming, very boring. Okay, cool, you pointed at this file, and it outputs these files. Excellent. But this is massively important. We could stop the presentation right now, because this gives you the ability to have require statements in your JavaScript! Which means if you have a file and you want to maybe split it into two pieces, re-factor your code like we would do in PHP, before, we would maybe not do that. Because if you split your JavaScript into two files, you have to add another script tag, or you need to go into some build system and remember to say, oh, now concatenate this file too, make sure they are in the correct order, all that kind of thing. It just didn't make sense. It was difficult to split your files.

With Webpack, you can actually program correctly. You don't think about the packaging of your files, you just think about: if I'm in one file, and I'd like to use another file, I require it. Very much like, again, I don't mean this to make it sound like the require statement is old, but in PHP, very much like we used to do in PHP. If you needed something, you required that file instead of just expecting it to be globally available.

CSS as a Dependency of your JavaScript

I'm going to put up a couple of best practices guides through using Encore. The first one, as you've seen, is you need to think of your CSS as a dependency of your JavaScript app. The same way the, that if you were in a JavaScript file, and you need another JavaScript file, you add the require statement. That's a dependency. Do the exact same thing with CSS. You say, in this JavaScript file, in order for the page to truly work, I need this CSS file. So, you require it.

One Global Entry

Another best practice is, and this is exactly what we've seen so far, is that you should have one entry, that means one source JavaScript file that's going to live in your layout. It's not a rule, but this is a best practice. This is exactly what we're doing right now, we have an app.js file, and that app.js file is included in our base.html.twig. It contains all of the global JavaScript and global CSS that we need for our site. Later, we'll talk about page-specific JavaScript and CSS.

Refactoring with require

The game-changing feature is that require statement. The ability to have that require statement. Which by the way is called, as soon as you start using require statements in JavaScript, suddenly your JavaScript files are called modules. When you hear module, it's just basically a JavaScript file that works in this system. This is just a simple example of how I would maybe re-factor my code. You have the app.js on top, and then I'm just going to require another file and use its function.

The key thing is, in the second file, is the module.exports. In PHP, when you used require statements, you would just require a file, and just receive whatever is inside that file. That's not the case with JavaScript, or Node. You actually need to export something. You need to say, I want to export this function, or I want to export this object, or something like that. We're exporting that function, and then we require it to import it.

Notice there is no .js on the random word, and that's just because JavaScript people really like making you be lazy. You can put the .js on the filename, but you don't need to. That's why you see it not there.

require() versus import()

Or, to make things a little bit more complicated, interesting. You see the require statement a lot, but the require statement is not cool anymore. You're supposed to now use this import keyword, and this export keyword. The reason I'm telling you this is so that you know that they are exactly the same. They are just two syntaxes that do the exact same thing. The import and export is actually more of a standard, so that's the one you should use. It has a little bit more flexibility, but really, they do the same thing. I'll typically use import and export. It's all the same thing.

Module-based Architecture... just like PHP

The best-practice now is to basically program like you would PHP. To organize your code into modules. In Symfony, we would organize our code into service classes to be well-organized, you can even unit test them. It's the same thing in JavaScript now. It's like: okay, I have this function or this object with some useful functions on it, let's just put that in its own file so that it's organized better. We can reuse it, and then we can just require it from wherever we need it.

Here's a slightly more complex example. This is a file that's going to just call a function, but it's requiring this displayRandomWord. Okay, let's look at displayRandomWord. That's just another function. Sorry, that exports a function, but it imports another file, and that last file is actually another function which actually gives us the random word. Just an example of the type of thing we would do in PHP typically: isolate these things into small pieces.

Ah, but there's a problem. We've already talked about this. CSS dependencies. Actually, let me go back real quick. This works great, but now I'm going to re-factor my code so that the displayRandomWord() function is now going to output HTML, and that HTML is going to have some classes on it. And dang it, I need to bring in the CSS file to style those classes. What we could do, because, remember our app.js file requires app.css, we could just go into app.css and add our class there. That would make it into the final file.

But we can dobetter than that. A better way is to actually isolate this into its own CSS file and require it directly from that module. What I'm saying here is: you'll typically see your main JavaScript file, app.js, require a CSS file. That doesn't mean that okay, great, let's put all of our CSS into that one file. No, we can actually break things down. We can have some very, very deep module - you don't even know what page it's going to be used on - but if that one module needs some CSS, like this, then require the CSS file. Then, no matter who uses this, you don't even care what page it's going to be used on, the CSS for that module is going to be included in the final output CSS.

Again, it's programming correctly. That's all it is. You're actually defining all of your requirements and dependencies in each little file.

Each Module is an Isolated, Unique Snowflake

The way you need to think about it is that each module, each file, is its own unique snowflake. Its own unique environment. When you look at a file, guys, I'm going to keep saying this, it's just like we program in PHP. If you went into it a file in PHP, you would never make any assumptions about what variables are available to you, or anything like that. If you need something inside of a class in PHP, you would make sure that you add a use statement, or use dependency injection, or something. It's the same thing with these modules. If you need something in a module, require it. Don't think: oh, it's okay, that CSS has already been required by this other module, which will be on the same page. That's bad. Put everything you need inside that one file.

To make things actually even a little more complicated, this is so cool, I love this, now I've taken that same CSS file, which is required by one of my JavaScript files, and now I need to point to a font file. Okay, what happens when we do that? It just works. Because Webpack is going to notice that you're referring to that font file, it's going to move it into the build directory for you, and the final output CSS is going to have the correct path to point to that font file. In fact, to Webpack, this looks like a require statement! It actually sees this, and it looks, to it, like you're requiring a font file. And so it says: oh, how do I handle font files? I move them into the build directory and make sure the path is set. The font file is a dependency of your CSS file.

In your CSS files you can use the @import syntax. In the top of some CSS file, you could say @import another CSS file. That's going to be read and parsed in exactly the same way. You could be in a CSS file and @import a SASS file, and that's going to go get processed just fine, and get processed through SASS.

Page-Specific JavaScript

Alright, so cool story. But, so far, we've only been talking about one file, one app.js file. More like we have one JavaScript file that we include on our entire site.

A lot of us still have multiple pages, so you have page=specific JavaScript. You have your main JavaScript and CSS, but let's say on your checkout page you have some pretty big JavaScript you don't want to put into your main JavaScript, because it's only needed on this one page. Okay, so now we're going to create a second file, checkout.js next to app.js. Same thing: we'll import the CSS we need. We'll import any JavaScript we need, write some code. This is just fake code, but you guys get the idea. Then we're going to go back into our Webpack config file. Remember, we haven't done much in this file yet. And we're going to add a second entry. An entry is an important concept in Webpack. Let's see here, and every entry results in one output JavaScript file and one output CSS file.

The result of this, since we added an entry called checkout, is that we end up with a checkout.js with all the JavaScript we need, and checkout.css with all the CSS we need. Then we just need to make sure that we put that on the checkout page. Inside of our checkout template, we're going to add a script tag for the one file, and a CSS link tag for the one CSS file.

The guidance on this is that, and of course, this is not an absolute rule, but if you're looking for general guidance, this is how I do it: is to treat each entry ... Well actually, let me say this a different way. Each page that needs its own JavaScript is going to get its own entry. It's going to mean, in practice, that every page is going to have the main entry, the app.js file that's in your layout, and if you need it, one other entry for that page-specific JavaScript. That entry file should contain all of the JavaScript, and all the CSS needed to power everything on your checkout page.

The other thing is, that each entry, this is how Webpack wants you to think about it, is its own standalone application. The Webpack, the authors of Webpack do a lot of single page apps, so they almost think of every JavaScript file as a single page app. You want to think of your checkout.js as its own app, which means that you need to, once again, require everything you need. If you need CSS require it, if you need some external library, require it. It's its own isolated environment. It's different than before when we think about: I'll include some script tags, and then these script tags will refer to some stuff that these script tags did. They're really two isolated environments.

jQuery: Things get Weird

Alright, so I want to talk a little bit about jQuery in case you're using it. Because jQuery is actually where things get weird. Actually, jQuery is also, because things get weird with jQuery, it's also a great example to understand how Webpack is doing some things internally.

Okay, so you want to use jQuery. This is one of the best things about the new way of developing. If you want jQuery, you just add it: yarn add jquery –– dev. Just add it: just like we composer require stuff. We don't need to download, go download something. We don't need to find a CDN. You just add it. Then you just require it or import it. That's it.

This is really great. Outside libraries are just actually very, very easy to use. This is not the problem with jQuery. This would work just fine. Anytime you import a module that does not start with a ./, it's importing it from the node_modules directory. If you are importing a local file, you've noticed I'm probably using ./ before: that means a file next to me. If there's no ./, it's coming from the node_modules directory.

jQuery is just like any other module, or React, or Vue. These are just modules: and you just require them, and they work like normal. Here's a key thing though, what's the difference between importing $ from jQuery and a script tag that you put in your layout for jQuery? The answer is ... everything. Even if that is literally pointing to the same file! Because, inside jQuery, and this is common to many, many modules, this is not a jQuery-specific thing, inside jQuery, it detects how it's being used and changes its behavior.

In Webpack, there are no global variables. Okay, just like PHP you can cheat and make global variables. But if you're programming things correctly, there are no global variables. When we include a script tag on the page, what does that do? It gives us a global jQuery variable. If you require it, it detects that, and it uses the module.exports: it returns a value. It does not actually give us a global variable. The key thing here is that most JavaScript libraries are going to change their behavior based on how they're being imported. It's just something that you need to understand as you're going from the old way to the new way of doing things.

A few minutes ago I talked about how you want your entry files, your application and your checkouts.js to function like two separate applications. This is interesting. If we import $ from 'jquery' in app.js, and its script tag is included first, and then in checkout.js we don't import it, but we just start using it, is that going to work? No. It's not going to work. Beautifully. That's going to be an "undefined variable $ in checkout.js": it's an uninitialized variable. In PHP, we would never expect that to work. It's not going to work. That is excellent.

This actually is little bit more interesting. Well actually, it's the same thing. Is this going to work? What I changed here is: okay, can I use the $ in maybe a template? I just need, hey, I'm getting lazy, and I need to put a script tag in my template. Is that going to work? Nope. Same thing, there's no global variable, so that's not going to work either.

One of the effects of using Webpack is that you will now have no JavaScript code in your template. Yes, we were always supposed to do that but we got busy, and lazy, and cheated etc. It's really not possible because you don't have any global variables. Now yes, you can cheat. In our tutorial on Encore we talk about that. When we upgraded SymfonyCasts to this, we actually set jQuery as a global variable, a true global variable, so that our legacy JavaScript would work. So that way, we didn't need to update everything all at once. Yes, you can work around this as you're updating your application.

jQuery Plugins: Weird gets Weirder

jQuery plug-ins are actually where things get truly weird. The weird thing about jQuery plug-ins, so bootstrap, I'm talking about the Bootstrap's JavaScript, it has some jQuery plug-ins in it, like tooltip.

The weird thing about jQuery plug-ins is that they don't return anything. They modify jQuery and add something to it. They work fine with Webpack, but they're clearly from a universe that existed before webpack. Because it's just weird. It's weird to just import bootstrap and suddenly we have a tooltip() function. It doesn't look obvious.

Internally, how does it do that? jQuery plug-ins, again, behave differently based on their environment. This is very important. If you think about the normal script tags, if you have a script tag for jQuery, then a script tag for bootstrap, how does bootstrap know where to find jQuery so that it can modify it? It only has one option, expect it to be a global variable. It just looks for jQuery as a global variable and it modifies it.

Fortunately, most modern libraries, most modern jQuery plug-ins now have code that looks like this. Where again, they detect their environment and they go: okay, I'm in a Webpack environment. What do they do? They actually require jQuery! One of the properties of the module system is that if two files require the same file, they get the same thing. It's a bit like Symfony's container. They'll get the same one instance of jQuery. It will actually modify jQuery.

Now, not all plug-ins are written correctly though. Here's a example. This is just a silly jQuery plug-in I found, tagsinput. The cool thing is I can say yarn add, so I can just add this to my project by saying yarn add jquery-tags-input. Great. I'm going to import the JavaScript file. That, in theory, will give me a tagsInput() function.

Also, this is a really cool thing. It's very common to have a JavaScript library that also has CSS with it. So normally we have to add one script tag and remember to go add the link tag. Now I just require the CSS file, and you're done. In this case, when you have the name of the module then / a path, it's just literally pointing at node_modules/that directory/ the path of the CSS file. Sometimes you have to do a little digging to be like, what's the path to the CSS file? Once you find the path, you just require it. Done.

This doesn't work. We did the exact same thing as we did a second ago with bootstrap, but it doesn't work. So you get jQuery is not defined. The reason is that, inside that module, it basically has code that looks like this. It just goes, jQuery. It just, hey, jQuery. It just expects it to be a global variable. And it's not anymore.

This is still written the old way. It has no code in it to make itself work in a module environment. It's broken. This is probably the most common and consistent question we get about Encore. It's not even an Encore thing, it's just a Webpack thing. It's important to understand how these jQuery plug-ins work, how they load, so that you can debug what's going on.

Ok so how do we fix that? Magic. We go back to our webpack config file, and we add one new line called .autoProvidejQuery(). This is incredible. And that function is an Encore feature, but anything in Encore, we're just leveraging features in Webpack. This is just leveraging a feature in Webpack. So what does this do? It rewrites the bad code. It literally, as it's going through all of the JavaScript files that you are working with, if it ever finds a jQuery variable that has not been initialized, it replaces it with require('jquery') and puts that in the output.

Yeah, right? It's incredible. This fixes it, and all of a sudden you can use these old things. Brilliant, we fixed somebody else's bad code! Be careful, because now we can write bad code too. This is now possible, so this is the downside of .autoProvidejQuery(). So, don't turn it on if you don't need it. It now means you can go into any file and just start saying $, or jQuery. You can instantly start programming the old way with undefined variables. And Yay, Encore will also fix our bad code. If you turn it on, try to not do this, even though you can.

This is important, if I'm in a Twig template, and I put an inline script tag, that still does not work. Because .autoProvidejQuery() does not give you a global jQuery variable. It rewrites any code that's processed by Webpack. If you just have some random Twig template, there is still no $ variable. This is just a repeat from earlier, even if you can cheat with the autoProvidejQuery() plug-in, remember that each file is its own environment, so remember to require it.

Entry != script Tag (in the old way of thinking)

This is another thing, so a couple of lessons from the past year that we've seen people do. How many people have had applications that look like this? Yeah, yeah, me too, yes. Because this is how we used to program. Require shared, and that creates these five global variables, and these 10 global functions, and then vendor.

Okay, now we have a jQuery global variable. We just build on top of each other by adding more and more global variables. Then we have some script on the bottom that actually uses these. I have seen people basically take their old setup and just move it directly into Webpack. I understand, every file that I have in my old application is just an entry file, right? Because this is going to basically result in the same output file. Yeah, first one requires a file, vendor is going to go actually require juery and react. Okay, good, this works, right? This does not work at all. Because what happens with that vendor entry, that vendor entry is going to require jquery. Good for you, you just basically gave yourself a jQuery variable and never used it.

It's like calling a function, setting a variable, and then going to lunch. Because that doesn't set a global variable. That's why I don't follow this model, I follow the model of one entry per page. Think about your checkout page as its own JavaScript application. What is all the code that needs to go into this to build this JavaScript application?

addStyleEntry(): It's a hack

Another thing, another feature that we've had forever in Encore is the addStyleEntry(). That's a way for you to say, oh, I want an output file, but it's just CSS. I just need a CSS file. That's a hack. We added that as a way to make people more comfortable, but you shouldn't use it. By shouldn't, I mean it's not like a bug, buggy or something, it's just that if you're using that, you're probably not organizing your code correctly. Because your CSS just shouldn't be just some random, hey, I just need a CSS file. You should be thinking what: JavaScript file is this CSS a dependency of?

In our app.js, we require the app.css file: this is the CSS that's needed for our layout, so we think of it as a dependency of the JavaScript file that's in our layout.

Splitting Files / New splitEntryChunks()

Okay, now this is where things get really interesting and we're going to talk about some of the new features of Encore. I realize I'm running a little low on time, but I also realize there is a break afterwards. So sorry if I keep you for a few extra minutes.

Alright, so Webpack says:

hey, it's cool, just require stuff, I'll handle all the details, don't think about it. Really, it's like don't think about it. You just write code correctly, I'll take care of the rest. I'll build your files perfectly.

Great Webpack, except, wow, those are pretty big files, those JavaScript files, yeah, 168 kilobytes. This is the development mode, so it gets smaller in production. But jeez, those are big. Because... we have so many jQueryies. Because we required jQuery from our app, and we require jQuery from our checkout, so what did webpack do? It put jQuery in both. Perfect! Except for performance on your front-end. How do we fix that?

This is not the way we fix it anymore. I wanted to show you this because you'll see this. This is the way that we fixed this problem for the first year and half in Encore. Because this is the way that you fixed it in Webpack. Again, we're always leveraging Webpack features. Webpack 4 came out earlier this year and changed a lot of things. This is one of the features that is still available in Encore, but is not the recommended way to do it. Yeah, I'm not even going to talk about it, but this is a feature that existed before. It still exists, but don't use it.

Now what? What we do now? I said don't use that feature. Okay, so introducing Webpack Encore 0.21.0. Wow, what a great version number for a big release! Wow, congratulations! This brought a lot of new stuff. Webpack 4 support. I'm going to talk about a few of these. I'll show you a couple of these, so I'm not going to mention all of them here. browserslist is a really good one. That allows you to put in your package.json file which browsers you need to support, and different parts of Webpack will know how to rewrite your code to be compatible with exactly those browsers. So, if you're using newer JavaScript features, or you need some vendor prefixing on some new CSS stuff, then it will automatically do that for you. Really, really cool. Webpack is always, and Encore has always done that rewriting, but it was more difficult before to control the exact browsers that you need for that. Yeah. The rest is not important, or we're going to talk about.

The Runtime Chunk

Real quick, this is not that exciting, but I want you to understand what it does. There's a thing called a runtime chunk. By the way, "chunk" is what Webpack calls a JavaScript file more or less. When you see chunk, that's kind of what it means.

This is a function that you can call now in your Webpack config file. Okay, cool, what does that do? It actually results in one additional file being output. A runtime.js. It now means that you actually need two script tags when you enable this. Why do we do that? There's two reasons. One is actually a little bit for performance. I don't want to get into the weeds too much. The runtime.js file contains some code that helps Webpack work. That code tends to change more often than your code, so by isolating it into its own file, your other files will change less often, and therefore can be cached longer by your users. It also has a side effect that when you have the runtime chunk, if you required jQuery from somewhere in app.js, and somewhere in checkout.js, they get the same object. Whereas, if you don't have that, your entries are so isolated that when you require jQuery, it's actually two separate objects. That may or may not be important to you.

Oh yeah, I actually have an example of that. Will this work? I require bootstrap in app.js. Down in checkout.js, is there a tooltip function? We required bootstrap further up, right? Right? It depends. With enableSingleRuntimeChunk(), yes, because they're actually using the same jQuery object. With disableSingleRuntimeChunk(), no, they would be more isolated.

It's not... what's wrong... enable is more convenient. Disable is actually a little more pure, because I said keep them isolated. It's up to you, I just want you to be aware of the decision there.


Okay, cool. Back to optimizing our build. We're not going to do this createSharedEntry() thing anymore. We're going to go back to just, we have 2 entry files, or maybe 10 entry files. Cool. Now we're going to say .splitEntryChunks(). This is all you need to do to optimize your build. You don't need to think about anything. Just call that function.

Okay, what does that do? That, when you run Encore now, you're going to get a little bit more output. And, if, you've probably never seen this before, but notice it says we have an entry point called app, and we have an entry point called checkout. Then it lists a bunch of files after each one. You'll notice after app, if you look, there's actually one, two, three, four JavaScript files listed after it. In order to get the app entry point to function, you now need four script tags. I know, yeah, I just got some looks like hmm?

What happens with splitEntryChunks(), is when you enable that, you ask Webpack to look at all of the files you're requiring across all your entry points, identify code that you're duplicating between the two, and try to figure out the most optimum way to split that into multiple JavaScript files.

It's really incredible how it does this. It takes into account your file size. If you have some shared code, but it's maybe like five kilobytes, it's not worth the extra web request to isolate that into a separate file. You can configure all this, so I'm just telling you the defaults. If it's above 30 kilobytes, I think that's the threshold that it decides that this is better in a separate file. It also distinguishes between your code and vendor code, things in node_modules, because it assumes that vendor code will change less often, so it tries to isolate the vendor code into its own file. Because that will change less often. Your users will, by isolating it, your users will be able to cache that longer because it's not going to change all the time.

It's actually a pretty incredible algorithm it's using to figure out the optimum way to do this. It also recognizes that your browser will make, it's either three or four parallel requests to the same host at the same time. It will split it to a certain point, but it realizes that if it keeps splitting it, then your browser's actually going to be waiting to download the first few JavaScript files before it starts the other JavaScript files. Yeah, it looks kind of crazy at first, but it actually works really, really well.

Of course, the problem is how do we know what script tags to include? Also, including four script tags, that seems like a real pain. Also, as you can tell, these are going to change. If you start doing something different, it's going to split it in a different way.

So, introducing the newest bundle in the Symfony family, WebpackEncoreBundle. Amazing! Amazing! Wow. Probably the smallest bundle in all of the Symfony ecosystem. It gives you two Twig functions and that's it. It's super cool. Now you just say, encore_entry_link_tags(), you give it the name of your entry, and it's just going to include all of the link tags, because the CSS is also split. Then same thing with script tags. It will include all of the script tags you need for that. When they change, will just get output.

How does that work? Magic? No. It's actually really boring. Oh, and same thing: checkout, include the checkout. It works because Encore dumps a file called entrypoints.json that looks like this. Just dumps exactly which files are needed for every entry point. That bundle just reads those and it works. This means that you just enable .splitEntryChunks() and you don't care. Things get split into pieces. It re-optimizes itself as you do different, keep coding and make more builds. Your code just works.

100% Cache Busting / Versioning

Also, I don't talk about here, but if you want versioning on your assets, so like when you build they have hashes in their filename, you get that out of the box. In the Encore recipe, we have a line in Webpack config that says enableVersioning(). All of your files output with a hash in the filename. And you don't even know or care, because those hashes end up in this file. And so as long as you use the Twig functions, then you get free versioning. If you change a file, then it's going to change the hash in the filename. You don't even think about versioning anymore. You just get it for free.

Long-Term Expiration Caching

That also means if you know a little bit about it, you can enable long-term expires headers for your assets. You can configure your web server to say, for all of my JavaScript and all of my CSS files, really, anything in this build directory, let the user cache that for a full year. Because I don't care. If the content changes, we'll change the filename. That can really massively speed up your frontend performance.

Dynamic / Async Code Splitting

One last thing I want to talk about, this is another feature that's not technically new with the new version of Encore, but we made it work without any configuration, is dynamic code splitting. It looks like this. Normally, we have the import function, the import call on top, the top of our file, we import all the things we need. Sometimes you have a situation where you have a large piece of code, and you only need that code under certain situations.

The perfect example is if you have a React or Vue router, and it's like when you go to this URL, render this component, go to this URL, render that component, if you go to this URL, render that component. If you just code that, normally, that means all of the code from all of your components will get packaged into one single file. Maybe not that big of a deal. It depends on how big your application is, how much you care. Instead, what you can do is you can use import like a function. It basically looks like an AJAX call, because it is an AJAX call. Import like a function, and then you give it the name of the module that you want to import, and then you say .then(), that's a promise, .then() and you pass it a callback. The argument passed your callback is that module. And then you use it.

In this case, since we're importing external linker, that code will not be included in the app.js file. Instead, the moment we need it, it's going to grab it via AJAX, and then when it finishes, it's going to go execute it. It also includes the CSS file, because our JavaScript down there required CSS. We don't care. It's just going to work.

In Conclusion

All right, so now putting all together, the things I want you guys to take away from this, the best practices are: create one entry file in your layout that's going to contain all your global JavaScript and CSS. Treat each entry you have like an individual application, my checkout application, my product list application. Organize your code. We can do that now. Finally. Finally we can actually organize our code properly into pieces. Remember to treat each module like its own unique environment. Require everything you need just from the very specific place you need it. Require the CSS you need from that tiny little module that actually needs it. Like I said, make your CSS a dependency of your application.

Okay, and I forgot this one: require jQuery like anything else, even if you are allowed to cheat because you use autoProvidejQuery(). And, use the new splitEntryChunks(), because that's going to make your life much easier. By the way, I showed most of the presentation, I showed using normal script tags and normal link tags. Then we re-factored to the bundle. In reality, you just use the bundle. When you use Encore, you use those functions, then you don't have to think about versioning, or splitEntryChunks(), or anything. It makes sense to turn that on.

All right, thank you, guys! Thank you for letting me go a little longer. Questions? I think I get to throw this. Cool. I was like, there has to be at least one question, because I haven't been able to throw this yet.

Yeah, that was amazing. That was on me. That was a bad throw. That was a good job over there.

Why are you wearing no shoes?

Why am I wearing no shoes? Well, now it's like my thing. A long time ago when I was presenting, I had shoes with heels, and I got on the stage, and it was like clunk, clunk, clunk, clunk. So, now I wear no shoes so I can be silent and slide around the stage. If it's summer, I wear no socks also.

Question over there? Or was it the same question?

Okay, my question is I'm not familiar with JavaScript, and I was wondering why you add –-dev everywhere.

Yeah, yeah, that's a really good question. Why when I'm doing the yarn add, like the composer require, why was I adding –-dev? It doesn't matter. Technically, it's just a technical detail. Technically, if you use Node on your application for Webpack, but you also actually had a little bit of Node that you actually ran in production. I don't know, your code actually went through and used some Node code, then in theory, by adding Encore and those things as Dev dependencies, when you're deploying, you would actually, that's, you would run Encore, and your dev dependencies would be there, and you'd get that final built public/build file. But then when you finally got to production, and you needed to install your Node dependencies for whatever weird thing you're doing at runtime, you could actually ask yarn to only install your not dev dependencies, which would be whatever libraries you're using for your actual runtime code. But you don't actually need Encore on production. It's technically correct as a dev dependency because that's not something that you actually need on production to execute your code. In reality, it doesn't matter because none of us, almost none of us are going to want to go to production and install our not Dev dependencies of Node because we have Node running alongside our PHP application. It's a weird edge case. Yeah, good question.

Nice, oh good, you guys are responsible for throwing it now.

Hi, thank you for presentation. I actually have two questions. First you said that require and import are equally the same, but they're not. You showed that there is asynchronous fetching in import. It's a big difference between the require also model splitting you can include only this part you need. The second question is how this jQuery fixing tool affects building time.

Interesting. Yeah, first part, yeah. You guys saw, I said require and import were basically the same, but import is a little bit better, but I didn't really say why. One of the reasons, as you said, is the import has this asynchronous, the import function thing. You can actually do that with require also, but the import is the cooler way to do it. The other thing which we didn't talk about is import and export, you have the ability to export multiple things from a module. With the require and the module.exports, it's always module.exports equals, the one thing that you want to export. But there's technically, with the export syntax you can export like 10 functions from the same module. Sorry, the other question was?

About jQuery fixing pack, or making them modules.

Oh yeah, the jQuery fixing thing. I don't think the jQuery fixing thing affects performance, or at least affects performance very much. The reason is that Webpack is basically already doing all that work to go through and parse every file and look for the require stuff. We also go through a tool called Babel, which actually reads your JavaScript code, and then outputs old JavaScript.

And changes imports to require, yeah.

Yeah, I don't think it affects much. Your builds can get big. It has to do with the size of your project. If you're doing things like... this alone won't make your builds slow, but if you were doing, if you were using SASS for CSS, and you wanted to import bootstrap as SASS, that alone is not going to make your build slow. But, if you start doing lots of those types of things, all of a sudden you're saying, hey SASS, go parse this giant SASS file. That's the kind of stuff that's going to make your build slower.

Thank you.

It's good you guys all sat together with the questions. It's very convenient.

I'm not into JavaScript very much, don't know very much information about it. In my company, we already moved to Webpack a couple of weeks ago, but I don't know why every time I get a new branch, without accessing or editing any JavaScript or CSS files, I can see the package.json already changes. I don't know why.

The package.json changes?


Yeah, I don't know about that. As he changes branches, the package.json file is suddenly modified. I'm just going to say that in case somebody else knows what weird thing that happens, but that might be something specific to your project.


Oh good, he can tell. Good.

Okay, so basically depends on the environment, so if some of your team, then you can have some differences in output. You can find a stackoverflow on basically how to fix it. You can disable it.

You better fix it in your project. So then you have no changes between operational systems. In our company we have fixed it recently, and it's pretty easy, you can just find it on stackoverflow.

Yep. All right, think we're past time. If you guys have more questions, come up and say hi. Thank you, guys.