Which UI do you use?

Custom UI

Pre built UI

Sending Requests with Fetch

Enable Fetch Interceptors

The init function call automatically adds interceptors to fetch. So there is nothing else that needs to be done.

Via NPM

import SuperTokens from 'supertokens-website';

// call this when your app starts
SuperTokens.init({
    apiDomain: "https://api.example.com"
});

async function doAPICalls() {
    try {
        // make API call as usual
        let fetchConfig = { /* ... */ };
        let response = await fetch("/someAPI", fetchConfig);

        // handle response
        if (response.status !== 200) {
            throw response;
        }
        let data = await response.json();
        let someField = data.someField;
        // ...
    } catch (err) {
        if (err.status === 401) {
            // redirect user to login
        } else {
            // handle error
        }
    }
}

Via Script Tag

supertokens.init({
    apiDomain: "https://api.example.com"
});

async function doAPICalls() {
    try {
        // make API call as usual
        let fetchConfig = { /* ... */ };
        let response = await fetch("/someAPI", fetchConfig);

        // handle response
        if (response.status !== 200) {
            throw response;
        }
        let data = await response.json();
        let someField = data.someField;
        // ...
    } catch (err) {
        if (err.status === 401) {
            // redirect user to login
        } else {
            // handle error
        }
    }
}