Conf42 JavaScript 2021 - Online

Incremental Static Regeneration: Static sites on steroids

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Static sites are great. They are fast, cheap, secure, and easy to maintain. But generating static assets is a process that takes more and more time while our site gets bigger. We will talk about Incremental Static Regeneration (ISR), a feature that Next.js framework offers us to generate static pages at runtime. With it, we get the benefit of static, but supporting dynamic data and page re-rendering on demand.

We will talk about static web pages, static site generation and, in particular, Next.js. We will present Next.js Incremental Static Regeneration (ISR). We’ll see how it works and code a little example.


  • Facundo Giuliani: A static web page is a web page that is delivered to the user's browser exactly as it's stored. Different is the case of the dynamic web pages where some of the content is generated dynamically when needed. There are a lot of options in the market depending on the market.
  • Nextjs generates the boilerplate that nextjs generates when we execute create next app. For server side rerendering we have the main function that generates the markup for our pages. The static site generation version of the page is using the same main function. When a user visits our website after 10 seconds we'll run the build process in the background.


This transcript was autogenerated. To make changes, submit a PR.
Hello everyone, my name is Fakundo and today we will talk about incremental static regeneration. First of all, I want to introduce myself. I'm Facundo Giuliani from Buenos Aires, Argentina. I'm a developer relations engineer at Storyblock. I'm also an odd serial ambassador, a prism ambassador and a clothingary media developer expert. It if you want to talk about any of these services or tools, or if you want to talk about any other thing, you can contact me. My website is and I'm on Twitter. My handle is fakundosurdo. So first of all I wanted to define what a static web page is. It is a web page that is delivered to the user's browser exactly as it's stored. So we can have a web page that has an HTML file, CsS file and JavaScript file that we will call it static page. If we are delivering the same files to all the users that visit our website no matter any condition. This doesn't mean that the content of the page ISR going to be static. I mean we can have interactions and dynamism, but we will use that or we will generate this using JavaScript, but the files that we are going to deliver to all the users that are visiting our website will be the same. Different is the case of the dynamic web pages, which are web pages where some of the content is generated dynamically when needed. So depending on the user that is visiting our website or other conditions, we will generate HTML content dynamically on the fly and we will return that to the user as if it were an HTML page that was statically stored on the website. The user won't know that we have two main methods of rendering this dynamically generated HTML content. One of these methods is the server sites rerendering, where the HTML content is generated by the web server and return it to the user as if it were an HTML file. But on the other hand, we have the client side rendering where the HTML content ISR rendered directly in the browser using JavaScript. So this will be the example of a react application, for instance, where we have JavaScript code being executed in the user's browser and generating HTML content dynamically. So we can choose these types of rerendering HTML content if we want to generate it dynamically, let's say. But let's go back to the static web page because even though this was the first type of web pages that we were able to create on the instance, they have some cool benefits that we can identify and that we can get advantage of even in these times in these years. For instance, static web page isr fast because we are delivering static assets to the users without doing any kind of processing or any dynamic generation of content. The static web pages are cheap because we will need sites, sorry, web servers that will store these static assets and deliver them to the users without doing any process. Or we don't need any calculus to be executed so they can only store the files and deliver them to the users that are visiting our websites. The static web pages are easier to maintain because as any other file system we can move sites from one side to the other. They are more secure because we are not executing code on the flight, so we don't have to worry about securing any kind of code execution. They are easy to scale because adding more storage space to our web servers we will be able to scale the static websites that we are working on. So for instance, if we have a blog and we are creating more and more articles and blog posts in our website, just adding more storage space to the web server will help us to scale our website. And they are stable because as we are not executing code or doing operations on the flight, the visitors will only have to download the files to their browsers and will browse the website. So that will make our website to work more stable. So having all these benefits in mind, a new concept was created. The concept of static sites generation which ISR compiling and rerendering a web application at build time, generating static assets like HTML, JavaScript and CSS files. So we will have a project with a templating engine. Depending on the programming language that we want to use, we can have different templates that we can use and besides these templates, we will have data sources like APIs that we can consume, headless CMS or content management systems. We can have databases, we can have processes that are being executed and based on these operations and these data sources and these templates, we will run a build process using a static site generator and we will generate static assets that are going to be my website, I mean my static website. So we can work with different tools, modern tools to create our projects and our websites and generate static assets as if it were a static sites like the ones that we created in the said. So there are different static site generators that we can use and there are a lot of options in the market depending on the framework or the programming language that you want to use today. I will focus on next JS which is a react framework that allows creating user interfaces, static pages and server side rendered pages. So we can create different pages using react components and all the features that react offers us. And next JS offers a page based way of working. So we will have one JavaScript file per page in our website or we can work with dynamic roots that one JavaScript file will generate multiple pages. Like for instance we can create one JavaScript file with nextjs code to generate all the blog posts that we can have in our blog site and we can use static site generation to generate all these static assets at build time. So we will have all the blog generated and it will be all static assets like HTML files, JavaScript files and CSS files and we can deploy that to the web server. So we will have our website using static assets, but we created it using JavaScript and a react framework like netjs. What is cool about nextjs is that it also offers other takes of rendering and generating HTML content like server side rendering or client side rerendering as we mentioned before. And it also offers API roots that we can use as serverless functions, for instance to execute an API, an operation and return information to our pages that we can use to render HTML content. And it also has a fast refresh on develop environment. So if we are working locally and we are working with the static sites generation mode, we don't have to wait to generate the static asset whenever we are making or applying a change to our code, we will have it automatically updated in our browser while we are working. Another cool thing that Nextjs offers is that we can work with the different types of rendering in a page level. So we can have some pages that are generated at build time using static site generation and other pages that can be generated using server side rendering or client side rerendering, all living in the same project in the same website. So for instance in the case of the blog, we can create the home page and probably the latest ten blog posts at build time as a static pages and we can have the older blog posts that probably will be visited by less users to be generated using server side rendering or client side rendering. If we want to offer the same experience in all the blog posts that we have in our website or our blog site, we can generate all of them using static site generator at build time. But here comes a problem. Because the process of generating the static assets takes some time and if our website is getting bigger and bigger with more and more pages, this build time will increase more and more. So in the case that we want to add a new blog post to our platform, or in the case that we want to edit one page to our website. If we want to generate all the static assets at build time, this process will take longer and longer. And besides that, there is a concept that is called atomic deployment, which means that if we are using static site generation, we have to generate all the static assets that we need at build time without errors. If there's any error in the middle of the process or if there isr a page that we are not generating statically, we will roll back all the process and we won't deploy this version of the website. This is done so we don't break the compatibility between the different pages and we don't have different pages or different versions of the pages living at the same time. So we have our blog or for example our ecommerce platform and we are increasing more and more products to the ecommerce platform and we are building the whole website whenever we add a new product or whenever we change something related to a product. And this build time is getting longer and longer and longer. And that's something that probably won't work for our scenario. So to solve this problem, NextJs now offers a new feature which is called incremental static regeneration. This feature enables developers to use static site generation on a per page basis without having to rebuild the entire site. So we will have the build process of the static site generator running for the first time and we will generate the version one of our pages, let's say after we generate all the pages that we need, we will deploy them to the web server and we will cache the first version of these pages. We will have a property called Revalidate that we can set in a steroids value so we can set for instance 60 steroids. In that period of time, all the users that visit our website will see the version that is cached of the pages, the first version. But if a visitor comes to our website and wants to visit a certain page after this revalidate time, nextjs will display the version one of the page, the one that is cached but in the background will execute a build process to regenerate only this page in the background, generate a new version and after that deploy that to the web server and cache this version. So all the following users that will visit this page will see this version two of the page. So in case that we are editing the content of this page or we fix the typo or we are adding some more content to the page. This is a cool feature because we don't need to reveal the complete site. We will have this revalidate time to work for us and to generate the new version of the page when we need it. So this offers us or disallowed us to have faster bills because in case that we want to generate just a set of static pages, or we can work with a higher cache so we can cache all the static assets of our website and generate all of them at build time, and after that generate one page at a time when it's needed, just when it's needed. This is cool that we can link this property to a headless CMS. So in case that we have a team of content editors working on our blog post for instance, or the content of our website and they are making changes. We don't have to run the build process whenever they apply a new change or whenever they create new content. We will just run the build process per page and when needed, I mean when a visitor comes to our website after this revalidate time. One other thing that incremental static regeneration offers is that the pages that are generated are persisted between deployments. So if we deploy new version of our website, we will persist the pages that we generated before using incremental static regeneration. This is a problem that we have to evaluate because we are breaking the atomic deployment doing this. I mean we will have pages of different versions living at the same time, but probably this is something that can help and we can solve a certain scenario using incremental static regeneration. I will show you a quick demo so you can see how each one of these rendering methods works. So what I'm going to do is go to this project, this page that I created a title and three features. We can see that I'm using a nextjs application that is running locally in my computer and I'm having the same content which will return the same page using three different methods of rendering, server side rendering, static site generation and incremental static regeneration. So we can see that this page is using server side rendering which is the content. This content is generated for every visitor that we will have in our website. I mean every user that code to our website, we will execute the code to generate the HTML content for them. Besides that we will have the static site generation method where we have here the same content. But this was generated at build time. When I run a build process at the beginning to generate the static assets with this example, probably you can see the benefit, but this page will load faster because we are not rendering any content on the flight like we did with the server side rendering. And finally we will display incremental static regeneration where this pages was generated at build time also. But if we run it again we have the revalidate feature running. But again as I didn't change any content you can see any change here. What I'm going to do now is show you the code of my application. This is a neck JS project. I don't want to go super deep into the folder structure of nextjs and how Nextjs works, but this is the boilerplate that nextjs generates when we execute create next app using npm in our local computer. So what we have here isr a pages folder and each one of these is the URL that we were visiting in the example that I just displayed. And these ones are Javascript files you can see with dynamic roots. We are using the slugs for the dynamic roots. So what we are doing in this particular case is for server side rerendering we have the main function here which is the one that generates the markup for our pages. We have some react components here that are using some story, that code from our headless cms which in this case is a storyblok. And I will show you storyblok in a couple of minutes and we are bringing information from the headless cms to render it on the page. So we have this main function that will generate the markup and we have a get server sites props function that is executed whenever a user visits our website. So in this code what we are doing is setting a slug variable with the home value because we are going to bring all the information related to the home page and well setting some parameters that we will send to the headless cms and using the storyblock client to get all the information related to that story. One story in storyblock is like a page, let's say. So we are bringing all the data, all the content for that page. We are returning that as a story and this return is going to the main function and using the story that we are sending to generate the content related to that story. We will execute this function for every user that visits our website. On the other hand, the static site generation version of the page is using the same main function. You can see that it's exactly the same, but we have a gets static props method or function that ISR executed at build time. When we run the static site generation process you can see that we are doing something very similar here. We are bringing all the data related to a certain story using the storyblok client and we return that to the main function. But the thing is, how do we identify which pages we want to render at build time. So to do that next, Js offers another function which is called get static paths. So what we are doing here is defining the logic that will generate the list of pages of pages that we want to generate at build time and generate the static assets related to them. As my project has only one page which is the home page, we are sending like a list of paths but with only one value which is home. So with this list we execute the get static props function for every value of this list and we will generate the markup. Finally, the incremental static regeneration page ISR, the main function is exactly the same and you will see that it's very similar to the one of the static site generation. Here we are doing exactly the same and here is very similar. But we are setting this property fallback to blocking and we are adding the revalidate value that we saw before in the slide and we are setting that to 10 seconds. So when a user visits our website after 10 seconds we'll run the build process in the background to generate a new version of the page. So let's see in this example what happens if I edit the content of the page. So let's go to storyblok which is the headless CMS. And you can see that. Well, Storyblok offers a visual editor, a real time visual editor that we can use to using the code of our application. You can see that it's pointing to my local host. We can on the flight do some changes and see how it's going to look like. So I can change this feature test and we can see that how it's going to look like without applying any change to the real content that we are consuming in our production instance, for instance. But if I click on Save, we are applying these changes to the draft version of our steroids or the content of our page of our website. So we have all the features that say now feature test. So I will go back to my example and I will first render the server side rendering page. What is happening? We are displaying the new content because we are rerendering this content for each time a user visits our web page. But on the other hand, if I use static site generation, we will see that we are seeing the old content because this page was generated at build time and I didn't run the build process again. So we have the version that was generated before as a static asset. So we don't notice that a change was applied to the content of the pages using incremental static regeneration we will see that we are displaying the old content that was generated at build time, like if it weren't edited or updated. But on the background we are executing a build process just for this pages. So I mean this visitor won't notice the changes or will see the old version of the page. But if I refresh the page here I will see the new content and I am seeing the version two of the page, let's say. And this will happen for all the following users that visit this web page, always considering the revalidate property and the value of this property that we set in the code of our application. So with this demo, I hope it's now clear for you how incremental static regeneration works. If you want to learn more about it, you can go to the Nextjs official website. They have an e commerce platform demo that you can take a look using incremental static regeneration. Or if you want to learn more about NextJs, they have a really cool learning platform that you can follow and learn other features from this very cool framework. So thank you very much. I hope you enjoyed the talk and see you there.

Facundo Giuliani

Developer Relations Engineer @ Storyblok

Facundo Giuliani's LinkedIn account Facundo Giuliani's twitter account

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