At this point, we’ve seen that because we wrapped our whole app in , any component in our application tree can get access to locale by using LocaleContext.Consumer. What React Context is allowing us to do is to define data stores and access them where they are needed. We talked a little about it in part one but let’s look at it again. // because it would have to be passed through all components. One way to solve this issue without context is to pass down the Avatar component itself so that the intermediate components don’t need to know about the user or avatarSize props: With this change, only the top-most Page component needs to know about the Link and Avatar components’ use of user and avatarSize. Let's take a look. For example, you can pass entire React components as props if you’d like to. Creates a Context object. To do this, Consumer uses a render prop. Updating Context in React from One Place We have to import context every time whenever we want to use or update the state from the useContext Hook in our React app. Notice, if you press the Toggle Component button, it will still toggle the GrandChild component. Suspense pour le chargement de données. The minimal example can be … Import createContext from react. Why, yes. Wow! Provider allows us to “declare the data that we want available throughout our component tree”. If the value is true, then it will render the GrandChild component. Here’s a very clever example my good friend chantastic came up with. const MyContext = React.createContext() const MyComponent = => { const { count, increment } = useContext(MyContext) return (

price: {count}

) } const App = => { const [count, updateCount] = useState(0) function increment() { updateCount(count + 1) } return (

… Now that we know the problem that Context solves, how do we use it? I made this tutorial also into a video, which can be found below: Interested in learning more about React and Javascript? In that case, it’ll get its value from the first argument that was passed to createContext when the Context object was created. Typically when you first learn about Context, it appears like it’s the solution to all your problems. Let’s look at the value within the Provider. Oof. Here's the function that changes the state. Awesome. Let's take a look. However, what if we also want to be able to toggle it (en -> es) from anywhere inside of our component tree? The way in which React knows if the data changes is by using “reference identity” (which is kind of a fancy way of saving oldObject === newObject). Congrats, my friend. Hooks allows you to use state, context and other React features inside functional components (i.e. This is totally out of control of the components using context, so there’s basically no way to reliably update the context. This is because you passed toggleComponent: this.toggleComponent in the value section of the Provider in the Parent component. Unless you are working on a very basic app you will need a way to update/change the data that comes from the React Context. When to add state to a Context, and how easy it is to retrieve and update the state. In this case, the component that is wrapped is the Child component. However, it’s a little different than part one of the tutorial. Then, create the Provider and Consumer. We will need something that is the alternative from the Mobx or Redux actions. Use the new context API introduced with version 16.3. Now, instead of just calling a function to toggle true or false, we’re actually passing a value to a function. Create the context. This section documents a legacy API. If it is true, then it will pass Bob to the switchNameHandler function. React has an API to update context, but it is fundamentally broken and you should not use it. // In this example, we're passing "dark" as the current value. #cleancode, #react As those have simple values like the others, you can store functions in your context. // The Toolbar component must take an extra "theme" prop, // and pass it to the ThemedButton. Hi and welcome back to part 2 of the React context API series. Technically though, you are updating the objects with the same initial values. In our example, that data is a. But now, we have the solution embedded into React. It’s the same Child component from part one! This is valid whatever level of component graph the children is in. We’ve created the Provider and the Consumer. Does this look familiar? This inversion of control can make your code cleaner in many cases by reducing the amount of props you need to pass through your application and giving more control to the root components. Remember, this is just a fancy if else statement. How do we access people? Vous pouvez aussi soutenir le blog sur Patreon. Now, any component in our component tree that needs the value of locale will have the option to subscribe to it using LocaleContext.Consumer. Just to remind you, the Context API allows data storage and makes it accessible to any child component who want to use it. In order to update data in the context, trigger a local state update with this.setState. // without explicitly threading it through every component. Just remember, there’s nothing wrong with passing props down multiple levels, that’s literally how React was designed. For more information about the ‘function as a child’ pattern, see render props. Can you guess what this does? But, now there is a button below it. For example, in the code below we manually thread through a “theme” prop in order to style the Button component: Using context, we can avoid passing props through intermediate elements: Context is primarily used when some data needs to be accessible by many components at different nesting levels. But wait… There’s a button? This will trigger a new context and changes will be received by the children. Create a Setter to update your Context’s state create a useUrl hook, which stores the state of the context, as well as updates it. class App extends React.Component { handleUpdate = () => { this.setState({}); }; render() { return (

{Math.random()}

< button onClick ={this. It’s also annoying that whenever the Avatar component needs more props from the top, you have to add them at all the intermediate levels too. Based on our example, we’ll create a LocaleContext. : null}, , context.state.toggleGrandChild ? The old API will be supported in all 16.x releases, but applications using it should migrate to the new version. This step is important. It could easily be written like this. The getChildContext function will be called when the state or props changes. The React Context API provides a way to pass data through the component tree without having to pass props down manually to every level. For example, one library that works this way is React Router V4: By passing down some information from the Router component, each Link and Route can communicate back to the containing Router. This blog post has a good explanation of why this is a problem and how you might get around it. The propagation from Provider to its descendant consumers (including .contextType and useContext) is not subject to the shouldComponentUpdate method, so the consumer is updated even when an ancestor component skips an update. It’s grabbing the value of toggleGrandChild from the Parent Component state. However, there are times when passing props through intermediate components can become overly redundant or downright unmanageable. const { Provider, Consumer } = createContext(). Remember what this function does? The legacy API will continue working for all 16.x releases. We will call our context AppContext: The newly created AppContext will be used to build a context provider component. use a context consumer where ever you need the data from the store.