You can verify this by assigning them to globals like window.SomeContext1 and window.SomeContext2 and then checking whether window.SomeContext1 = window.SomeContext2 in the console. This can happen if you use symlinks, for example. You might be running into some build issue with your tooling that causes SomeContext as seen from the providing component and SomeContext as seen by the reading component to be two different objects. The React Context API, introduced in React v.16.3, allows us to pass data through our component trees, giving our components the ability to communicate and share data at different levels.Check whether the hierarchy is right using React DevTools. You may have forgotten to wrap your component with, or you might have put it in a different part of the tree than you thought.Move above and outside the component calling useContext(). You’re rendering in the same component (or below) as where you’re calling useContext().There are a few common ways that this can happen: Troubleshooting My component doesn’t see the value from my provider Import Īs a result of this change, even if MyApp needs to re-render, the components calling useContext(AuthContext) won’t need to re-render unless currentUser has changed. Passing something via context only works if SomeContext that you use to provide context and SomeContext that you use to read it are exactly the same object, as determined by a = comparison.Ĭall useContext at the top level of your component to read and subscribe to context. If your build system produces duplicates modules in the output (which can happen with symlinks), this can break context.Skipping re-renders with memo does not prevent the children receiving fresh context values. These new documentation pages teach modern React and include live examples: Passing Data Deeply with Context useContext The new docs will soon replace this site, which will be archived. The previous and the next values are compared with the Object.is comparison. React automatically re-renders all the children that use a particular context starting from the provider that receives a different value.If re-rendering the component is expensive, you can optimize it by using. The corresponding needs to be above the component doing the useContext() call. A component calling useContext will always re-render when the context value changes. useContext() call in a component is not affected by providers returned from the same component.
React automatically re-renders components that read some context if it changes. If there is no such provider, then the returned value will be the defaultValue you have passed to createContext for that context. It is determined as the value passed to the closest SomeContext.Provider above the calling component in the tree. UseContext returns the context value for the calling component. The context itself does not hold the information, it only represents the kind of information you can provide or read from components. SomeContext: The context that you’ve previously created with createContext.
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