getAssetInBase64.ts

/**
 * Transforms blob to base64 using FileReader API.
 * @param blob - A blob instance.
 */
const fromBlobToBase64 = (blob: Blob): Promise<string> => {
  return new Promise((resolve, reject) => {
    const reader = new FileReader();

    reader.onerror = (): void => {
      reject(reader.error ?? new Error('Unknown error on FileReader.'));
    };

    reader.onload = (event: ProgressEvent<FileReader>): void => {
      const data = event.target?.result;

      if (typeof data !== 'string') {
        reject(new Error('FileReader returned non-string data.'));
        return;
      }

      resolve(btoa(data));
    };

    reader.readAsBinaryString(blob);
  });
};

/**
 * Receives a path of asset location, fetch is as blob and transform to base64.
 * @param path - Path to asset location.
 */
const getAssetInBase64 = (path: string): Promise<string> => {
  return fetch(path)
    .then(response => response.blob())
    .then(fromBlobToBase64);
};