What we're saying is if there are IDs present, we're going to want to set an IDs property on the Next data object. You might receive some advantages from using the babel-plugin however documentation on SSR state that it should work out of the box. Here, we're going to add a title. These names arent a part of the useState API.
Help Provide Humanitarian Aid to Ukraine. #dommanipulation, #javascript 
They let you use state and other React features without writing a class. #javascript If some things didnt quite make sense or youd like to learn more in detail, you can read the next pages, starting with the State Hook documentation. I'm going to say export default class custom doc, and it's going to extend that document that we just imported above. Saved by Next.js Official Examples - with-styled-components. This is a fast-paced overview. What that's going to do is make sure that the correct HTML, and IDs, and CSS that's needed for Emotion to render on the server is being mixed in to the object being created with that render page function. React will preserve this state between re-renders. useState returns a pair: the current state value and a function that lets you update it. Sometimes, we want to reuse some stateful logic between components. Custom Hooks let you do this, but without adding more components to your tree. This is a result of our styles not being rendered on the server. If we look at the page, we'll see these come to life. Now we actually are looking good. Its similar to this.setState in a class, except it doesnt merge the old and new state together. (We dont recommend rewriting your existing components overnight but you can start using Hooks in the new ones if youd like.). You can also check out the Hooks API reference and the Hooks FAQ. This is what executes the actual rendering logic within our application. Instructor: [00:01] Inside this index.js file, we see them using some custom components created with the Emotion JS library. If a functions name starts with use and it calls other Hooks, we say it is a custom Hook. Just create a .babelrc file at the root of your file and write: That's it, with this you'll achieve SSR for your styes. This will allow us to cache the IDs being loaded and prevent Emotion from doing any extra work. Effects may also optionally specify how to clean up after them by returning a function. Hooks are a way to reuse stateful logic, not state itself. We understand these rules might seem limiting or confusing at first, but they are essential to making Hooks work well. [01:36] The first thing we're going to do is hook in a Next getInitialProps lifecycle hook. #promises Well come back to why this works and when this is useful later. By default, React runs the effects after every render including the first render. #jquery, #javascript To do this, we need to create a file titled _document.js and place this inside of our pages directory. Follow the example here: https://github.com/zeit/next.js/tree/canary/examples/with-emotion. The useSomething naming convention is how our linter plugin is able to find bugs in the code using Hooks. Following this, we'll also need to import the extractCritical function from the Emotion server library. Custom Hooks are more of a convention than a feature. #parameters, #javascript That said, I'm pretty sure that it's no longer necessary to modify the .babelrc file. We'll use this with the extractCritical function in order to make sure that we're only injecting the necessary HTML within our app. Components in this lesson are built using the emotion-js library. In a moment, we'll see how we can effectively use these IDs to rehydrate our styles on the client. They link to detailed explanations. In this case, we just have this index.js file. Inside here, we're first going to import the hydrate function from Emotion. [02:12] Following this, we're also going to create a styles constant and set that equal to extractCritical, to which we're going to pass in the HTML that the renderPage function is giving us. #jsfunctions Each section ends with a yellow box like this. Earlier on this page, we introduced a FriendStatus component that calls the useState and useEffect Hooks to subscribe to a friends online status. Hooks are backwards-compatible. This setup isn't necessary anymore however it was at the time that this lesson was created. [01:03] The first thing we need to do here is import the document that we'll be extending, as well as the head, main, and Next script components. [04:37] It's going to format this quick. [01:50] Inside the custom document, this context object also holds a renderPage function. [00:22] You don't have to be a UX specialist to realize that this isn't going to give you a fantastic user experience. Note that unlike this.state, the state here doesnt have to be an object although it can be if you want. You can learn more about useEffect on a dedicated page: Using the Effect Hook.
This is only going to need to be called on the client. Lets say we also want to reuse this subscription logic in another component. We call it inside a function component to add some local state to it. [01:20] Now that we have this imported, we can go ahead and extend Next custom document class. However, if we refresh, we'll see that it loads the application without our styles being applied. Nowadays this is not needed. [03:57] Right now, it's pretty much what the custom document is going to look like by default. For example, useContext lets you subscribe to React context without introducing nesting: And useReducer lets you manage local state of complex components with a reducer: You can learn more about all the built-in Hooks on a dedicated page: Hooks API Reference. [05:31] Now, if we go and visit our browser again and we hit refresh, we no longer see that black and white HTML as our styles are indeed being rendered on the server. The initial state argument is only used during the first render. #nodejs [03:03] To do this, we'll first call super on our props and then pull of this Next data and IDs property off of it. By default, Next.js is going to use a custom document where it's going to set all the markup like the application's HTML and body tags, as well as the HTML that's being injected. Hooks are JavaScript functions, but they impose two additional rules: We provide a linter plugin to enforce these rules automatically. #javascript You can also create your own Hooks to reuse stateful behavior between different components. The only argument to useState is the initial state. You can write custom Hooks that cover a wide range of use cases like form handling, animation, declarative subscriptions, timers, and probably many more we havent considered. #nodejs, #javascript (Well show examples comparing useEffect to these methods in Using the Effect Hook.). We can just pass in window.nextdata.ids in order to use any cached IDs. In here, we'll use the dangerously set inner HTML prop. The Effect Hook, useEffect, adds the ability to perform side effects from a function component. [02:26] We can then just return page as well as styles using the spread syntax. Hooks dont work inside classes they let you use React without classes. Finally, dont miss the introduction page which explains why were adding Hooks and how well start using them side by side with classes without rewriting our apps. Basically using babel-plugin-emotion you are able to avoid any modification to _document.js. Effects are declared inside the component so they have access to its props and state. (Well talk more about how this compares to class lifecycles in Using the Effect Hook.). When you click the button, it increments the value: Here, useState is a Hook (well talk about what this means in a moment). As I mentioned earlier, this is where we add our HTML markup.
For example, this component uses an effect to subscribe to a friends online status, and cleans up by unsubscribing from it: In this example, React would unsubscribe from our ChatAPI when the component unmounts, as well as before re-running the effect due to a subsequent render. This example renders a counter. For example, this component sets the document title after React updates the DOM: When you call useEffect, youre telling React to run your effect function after flushing changes to the DOM. Hey Felipe, thanks for pointing out! Youve likely performed data fetching, subscriptions, or manually changing the DOM from React components before. Well look at the built-in Hooks first. This page provides an overview of Hooks for experienced React users. You can learn more about custom Hooks on a dedicated page: Building Your Own Hooks. Instead, React assumes that if you call useState many times, you do it in the same order during every render. In the example above, it is 0 because our counter starts from zero. [02:49] To effectively style our application, we also need to grab the props for many child components being loaded. // Similar to componentDidMount and componentDidUpdate: // Update the document title using the browser API. Luckily for us, Next.js makes the process of fixing this extremely easy. #javascript
Traditionally, there were two popular solutions to this problem: higher-order components and render props. React provides a few built-in Hooks like useState. [00:46] In order to render our styles on the server, we need to override the document's custom behavior. You can learn more about these rules on a dedicated page: Rules of Hooks. You can use the State Hook more than once in a single component: The array destructuring syntax lets us give different names to the state variables we declared by calling useState. #howto, open_in_newInstructions on embedding in Medium, How to Save HTML Form Data in JSON - Express, Add event listener to multiple buttons with the same class, 3 Ways To Detect Selenium Bots Using Javascript - CodingTutz, getAttribute() - how to get the value of any attribute of HTML element, Save to MongoDB without Duplicates Using Mongoose, Required Parameters for Functions in JavaScript, Detect click outside element (vanilla JavaScript) - Stack Overflow, How to Get the Domain From A URL Using Javascript. [04:48] Before we check this out though, we first want to make any modifications to any files within our pages directory. Phew, that was fast! The state of each component is completely independent. getInitialProps is going to return a context object including the response and request, and other properties helpful for when developing with Next. You can call this function from an event handler or somewhere else. We call these operations side effects (or effects for short) because they can affect other components and cant be done during rendering. Oops, I have to return this, or else it's not going to work. #functions // Declare a new state variable, which we'll call "count". [03:31] The last thing we need to do is return the markup for our document. We'll have all this React within the HTML tags, and then inside of our body tags, we're going to place the main, as well as the Next script imports, which is going to inject the proper HTML and load our scripts.
@GodFather Here, we'll say HTML is equal to this.props.css. #nodejs, #javascript Hooks are a new addition in React 16.8. [04:14] More importantly, we're going to need to add a style tag within our head. Just like with useState, you can use more than a single effect in a component: Hooks let you organize side effects in a component by what pieces are related (such as adding and removing a subscription), rather than forcing a split based on lifecycle methods. (If you want, theres a way to tell React to skip re-subscribing if the props.friend.id we passed to ChatAPI didnt change.). [05:09] Additionally, we'll need to pass in the IDs being created by extractCritical within our document component into this hydrate function. As we know, we're attaching those IDs to the Next data object. In this lesson, we learn how to modify Next.js' custom Document to ensure that our custom components are rendered on both the client and the server. We are excited to see what custom Hooks the React community will come up with. #dom As a result of this, all the style that's being created with Emotion will effectively be loaded right around the server. You can learn more about the State Hook on a dedicated page: Using the State Hook. In fact, each call to a Hook has a completely isolated state so you can even use the same custom Hook twice in one component. #javascript, #html It serves the same purpose as componentDidMount, componentDidUpdate, and componentWillUnmount in React classes, but unified into a single API. (Well show an example comparing useState to this.state in Using the State Hook.). [05:43] One thing to point out is that although we used Emotion in this lesson, we could have just as easily set it up with glamor or styled components by extending the custom document just like we did in this lesson. I am going to call it SSR with Next.js, and then Emotion.js. Hooks are functions that let you hook into React state and lifecycle features from function components. #commandline, #html First, well extract this logic into a custom Hook called useFriendStatus: It takes friendID as an argument, and returns whether our friend is online. If you get confused, look for a yellow box like this: Read the Motivation to learn why were introducing Hooks to React. There are a few less commonly used built-in Hooks that you might find useful.