test.js

getDataCached('a').then(result => { console.log('first call outer: ' + result);
    getDataCached('a').then(result => { console.log('first call inner: ' + result); });
});

getDataCached('b').then(result => { console.log('first call outer: ' + result);
    getDataCached('b').then(result => { console.log('first call inner: ' + result); });
});

getDataCached('a').then(result => { console.log('second call outer: ' + result);
    getDataCached('a').then(result => { console.log('second call inner: ' + result); });
});

setTimeout(() => {
	getDataCached('a').then(result => { console.log('later call outer: ' + result);
    getDataCached('a').then(result => { console.log('later call inner: ' + result); });
});
}, 70000);