const rp = require('request-promise');

const getToken = () => {
return getMySavedToken().then((token) => { // Assume your getMySavedToken API returns a Promise.
if (token && hasExpired(token)) { // If token hasn't expired.
return token;
}
return rp.get('Get a new token here').then((body) => {
return JSON.parse(body).access_token;
});
});
};

getToken().then((token) => {
// use my token
}).catch((err) => {
// Oops, something's wrong!
});