fileReader.js

export default file => {
  const fileReader = new FileReader();

  return new Promise((resolve, reject) => {
    fileReader.onerror = () => {
      fileReader.abort();
      reject(new Error('Problem parsing file'));
    };

    fileReader.onload = () => {
      resolve(fileReader.result);
    };

    fileReader.readAsText(file);
  });
};