Nadeem Shareef
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Context API with TypeScript and Next.JS

How to write context API with TypeScript and next.JS

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Why we need context?

In a typical React application, data is passed top-down (parent to child) via props, but such usage can be cumbersome for certain types of props (e.g. locale preference, UI theme) that are required by many components within an application. Context provides a way to share values like these between components without having to explicitly pass a prop through every level of the tree. read more

What is contextAPI?

Context provides a way to pass data through the component tree without having to pass props down manually at every level.

So, now we know why we need context and what is context let's dive into the coding part.

Before starting, set up a basic version of the nextJS app with typescript



npx create-next-app context-api
npm install --save-dev typescript @types/react
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Create a folder called context, here we will store all the different contexts. For now, create an AuthContext.tsx file

Step 1:- Create context type

Inside AuthContext.tsx.
As we are using TypeScript we have to create types for our context



type authContextType = {
    user: boolean;
    login: () => void;
    logout: () => void;
};
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Step 2:- Create context default values 



const authContextDefaultValues: authContextType = {
    user: null,
    login: () => {},
    logout: () => {},
};
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Step 3:- createContext & useContext 



const AuthContext = createContext<authContextType>(authContextDefaultValues);

export function useAuth() {
    return useContext(AuthContext);
}
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Step 4:- Create a provider function 



type Props = {
    children: ReactNode;
};

export function AuthProvider({ children }: Props) {
    const value = {

    }
    return (
        <>
            <AuthContext.Provider value={value}>
                {children}
            </AuthContext.Provider>
        </>
    );
}
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We will wrap this AuthProvider function, where we want to use our context, and the value prop will have the values of authContextType. We will fill up values in the next step.

Step 4:- Fill up values 



export function AuthProvider({ children }: Props) {
    const [user, setUser] = useState<boolean>(null);

    const login = () => {
        setUser(true);
    };

    const logout = () => {
        setUser(false);
    };

    const value = {
        user,
        login,
        logout,
    };

    return (
    ...
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Now our context is ready to use.

Step 5:- Enable AuthProvider

First, we have to enable AuthProvider, to do so edit the default _app.js file like so



import { AuthProvider } from "../context/AuthContext";
import "../styles/globals.css";

function MyApp({ Component, pageProps }) {
    return (
        <>
            <AuthProvider>
                <Component {...pageProps} />
            </AuthProvider>
        </>
    );
}

export default MyApp;
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Step 6:- Using context

Now remove all the template nextJS generate and simply import the context



import Head from "next/head";
import styles from "../styles/Home.module.css";
import { useAuth } from "../context/AuthContext";

export default function Home() {
    const { user, login, logout } = useAuth();

    return (
        <div className={styles.container}>
            <Head>
                <title>Context-api with TypeScript and nextJS</title>
                <link rel="icon" href="/favicon.ico" />
            </Head>
            <main className={styles.main}>
                <div>
                    <h1>Hello Context</h1>
                    <h2>User: {user ? "login" : "logout"}</h2>
                    <div>
                        <button onClick={login}>Login</button>
                        <button onClick={logout}>Logout</button>
                    </div>
                </div>
            </main>
        </div>
    );
}
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Okay many things happen here let me break it down, first we import the context hook "useAuth" then inside our Home() we destructure all the values from "useAuth" then we use it as per our requirement.

See the live demo
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