var { NativeModules } = require('react-native');
var obj = {
    uri, // either an 'assets-library' url (for files from photo library) or an image dataURL
    uploadUrl,
    fileName,
    fileKey, // (default="file") the name of the field in the POST form data under which to store the file
    mimeType,
    headers,
    data: {
        // whatever properties you wish to send in the request
        // along with the uploaded file
    }
};
NativeModules.FileTransfer.upload(obj, (err, res) => {
    // handle response
    // it is an object with 'status' and 'data' properties
    // if the file path protocol is not supported the status will be 0
    // and the request won't be made at all
});