refreshTokens.js

export const refreshTokens = async () => {
  try {
    const credentials = await getSpotifyCredentials() //we wrote this function above
    const credsB64 = btoa(`${credentials.clientId}:${credentials.clientSecret}`);
    const refreshToken = await getUserData('refreshToken');
    const response = await fetch('https://accounts.spotify.com/api/token', {
      method: 'POST',
      headers: {
        Authorization: `Basic ${credsB64}`,
        'Content-Type': 'application/x-www-form-urlencoded',
      },
      body: `grant_type=refresh_token&refresh_token=${refreshToken}`,
    });
    const responseJson = await response.json();
    if (responseJson.error) {
      await getTokens();
    } else {
      const {
        access_token: newAccessToken,
        refresh_token: newRefreshToken,
        expires_in: expiresIn,
      } = responseJson;

      const expirationTime = new Date().getTime() + expiresIn * 1000;
      await setUserData('accessToken', newAccessToken);
      if (newRefreshToken) {
        await setUserData('refreshToken', newRefreshToken);
      }
      await setUserData('expirationTime', expirationTime);
  } catch (err) {
    console.error(err)
  }
}