Get React Native Available Disk Space

rndispace.txt

// ios
RNFetchBlob.fs.df().then( response => {
  console.log('Free space in bytes: ' + response.free);
  console.log('Total space in bytes: ' + response.total);
});

// android
RNFetchBlob.fs.df().then( response => {
  console.log('External free space in bytes: ' + response.external_free);
  console.log('External total space in bytes: ' + response.external_total);
  console.log('Internal free space in bytes: ' + response.internal_free);
  console.log('Internal total space in bytes: ' + response.internal_total);
});

Source: 
https://stackoverflow.com/questions/41799211/checking-for-available-disk-space-in-react-native