Astro Crash Course #12 - Client Islands (React)

Okay, then my friends. So far, when we've been using Astro, I've said several times that after the site gets built and deployed, no JavaScript gets sent to the browser by default. And so naturally, Astro sites are generally fast in performance. However, sometimes you need some interactivity in the browser. For example, clicking a like button on a post which then updates in real time in the browser how many likes that post has. So in cases like this, you'll need some JavaScript to add that interactivity in the browser. Now to accommodate this, Astro utilizes something called Island architecture, where we can essentially add islands, client islands of interactivity to an otherwise static page. So if you take a look at this diagram of a web page, you can see we've got several sections on there that are static, right? Like a sidebar, uh the main content, and the footer. And it also includes a couple of interactive sections that might require JavaScript in the browser. So this page would be pre-built and rendered by Astro at build time as normal to include all these different static sections. And unless we state otherwise, sections as well. Then when the page reaches the browser, those islands can be hydrated and sent the JavaScript needed for them to work. So the idea is to keep as much of the site or page as possible static content and then only add the islands where we absolutely need that interactivity. And these islands can be built and added to your project using libraries like React or Vue or Svelte, which specialize in that browser interactivity. So then, let's head back to the code and try a little example. So then, what I'm going to do is add a little like button to the review page so that a user can click it and then that's going to update some local state in the component to update how many likes the review has. And we'll be using React to make this component. Now in reality, this component might reach out for a database like Firebase or Supabase, or it could just hit your own endpoint to run some logic on the server. Uh but for the sake of learning about client islands and how to make them, we're just going to use some dummy data instead. So then, how do we make a client island? Well, first of all, we need to install the library we want to use for the island, which is in this case React, and then integrate it with Astro. Now the easiest way to do that is by using an Astro integration maintained by Astro, and there's integrations for several different libraries including uh React, Svelte, Vue, Solid, Alpine, etc. So we can install the React integration by coming to the terminal. And you can see I've already stopped the dev server so I can install this. And then we type NPX Astro add, followed by the integration name, which is React. Then we can hit enter. Next, it's going to ask us if we want to install these packages, which we do, so we can hit enter to select yes on that. Then it's going to ask us if we want Astro to update the config file to register this new integration, which we do, so I'm going to hit enter again. And then finally, Astro wants to add some compiler options to the TS config file so that we can use JSX, so we'll hit enter once more to select yes for that as well. And now, just like magic, we can use React in the project. So then, let's make a new React component, and it can go in the same place as the other components. You don't have to have a separate folder. I'm going to create a new file inside the components folder right here, and I'm going to call this likes and then. tsx. And this is not going to be a tutorial about React. If you want to learn about React, I've got plenty of tutorials all about that on my YouTube channel or on netninja. dev. Instead, what I'm going to do is just paste in this React component. I will quickly go through it. First of all, we're importing use state from React. That's a hook that we can use to manage some local state in the components. So the component name is right here, this function called likes. Then we have this state called likes, and then we have a function to update the state called set likes, and the initial value is three. I've just plucked that uh from thin air. It could be whatever you want. It doesn't really matter. Then down here, we return the template for this component, so it's a div with a class name of likes. And then we have a paragraph tag right here that outputs the likes in curly braces, so that's going to be three to begin with, right? And it says that many people like this review. Then we have a button that says we want to like this, and when we click on this button, it's going to fire this handle click function. Inside here, we run this set likes function to update the like state. We take the previous value and we add one to that each time. So it's going to go to four, then five, and so forth. So I also want to just add a little bit of styling for this as well. And I'm going to do that inside the global styles within the layout right here. So let me come down to the global style tag, which is this one. And at the bottom, I'll paste in just a little bit of styling, so we grab that class likes, so we give it a border top, etc. Then we style the button inside that as well. All very simple. Okay, so now we've got the React component made, and we want to use it in the application on the book details

page. So let's open that page up, and the first thing we need to do is import the like component at the top of the front matter, and we can do that by saying import likes, and that comes from two folders up, so dot forward slash, then another into the components folder, and then we want the likes file. After that, we can use it in the template. So let's come to below the content component, and we're just going to add it in right here. Now then, if we save this and preview, then we will see the templates of this likes component in the browser. And that's because Astro still pre-builds the React component and adds it to the page by default. But it also strips out all of the JavaScript by default as well. And if we scroll right down this page, we should eventually be able to see the component which has already been rendered. But when we click on the button, nothing happens because again, by default, Astro doesn't ship any JavaScript to the browser. It strips it all out of the components. So the way we can tell Astro to send the JavaScript is by adding an attribute to the component where we use it, which is client, followed by a colon. And then we've got a couple of options. We can use the load option, which tells Astro to load the JavaScript for this component and hydrate it immediately when the page reaches the browser. Or what I prefer using is the visible option, which tells Astro only to load the JavaScript in the browser and hydrate the component when this component is visible on the page. Because it's sitting right at the bottom of the page content. So it makes sense to only load it when a user scrolls all the way down and they can see it, right? So I'm going to save this now, then we'll try it out. Okay then, so I've already refreshed the page and I've cleared the network tab to show you how the JavaScript only gets loaded when we scroll down enough to see the component. So if we keep on scrolling, eventually we're going to be able to see it, and all the files and JavaScript needed for the component get loaded in. And now if we press the like button, we should see that everything is working. Awesome. Okay, so in reality, rather than hardcoding the React state, you'd probably be getting those numbers from a database or something, and that's fine. Nothing changes except for your logic in the React component to do that. And we'd still load it into the page the same way. So hopefully, you've got an idea now about how client islands work in Astro. I think they're a really cool idea, and they let us sprinkle in that interactivity only when we really need it, using whatever framework that you prefer.