Download a blob with TypeScript

  • Article

This article shows how to download a blob using the Azure Storage client library for JavaScript. You can download blob data to various destinations, including a local file path, stream, or text string.

Prerequisites

  • The examples in this article assume you already have a project set up to work with the Azure Blob Storage client library for JavaScript. To learn about setting up your project, including package installation, importing modules, and creating an authorized client object to work with data resources, see Get started with Azure Blob Storage and TypeScript.
  • The authorization mechanism must have permissions to perform a download operation. To learn more, see the authorization guidance for the following REST API operation:

Download a blob

You can use any of the following methods to download a blob:

Download to a file path

The following example downloads a blob by using a file path with the BlobClient.downloadToFile method. This method is only available in the Node.js runtime:

async function downloadBlobToFile(
  containerClient: ContainerClient,
  blobName,
  fileNameWithPath
): Promise<void> {
  const blobClient = await containerClient.getBlobClient(blobName);

  const downloadResult = await blobClient.downloadToFile(fileNameWithPath);
  if (!downloadResult.errorCode) {
    console.log(
      `download of ${blobName} success ${downloadResult.blobCommittedBlockCount}`
    );
  }
}

Download as a stream

The following example downloads a blob by creating a Node.js writable stream object and then piping to that stream with the BlobClient.download method.

async function downloadBlobAsStream(
  containerClient: ContainerClient,
  blobName,
  writableStream
) {
  const blobClient: BlobClient = await containerClient.getBlobClient(blobName);

  const downloadResponse = await blobClient.download();

  if (!downloadResponse.errorCode && downloadResponse?.readableStreamBody) {
    downloadResponse.readableStreamBody.pipe(writableStream);
    console.log(`download of ${blobName} succeeded`);
  }
}

Download to a string

The following Node.js example downloads a blob to a string with BlobClient.download method. In Node.js, blob data returns in a readableStreamBody.

async function downloadBlobToString(
  containerClient: ContainerClient,
  blobName
): Promise<void> {
  const blobClient: BlobClient = await containerClient.getBlobClient(blobName);

  const downloadResponse: BlobDownloadResponseParsed =
    await blobClient.download();

  if (!downloadResponse.errorCode && downloadResponse.readableStreamBody) {
    const downloaded = await streamToBuffer(
      downloadResponse.readableStreamBody
    );
    if (downloaded) {
      console.log('Downloaded blob content:', downloaded.toString());
    }
  }
}
async function streamToBuffer(readableStream) {
  return new Promise((resolve, reject) => {
    const chunks: Buffer[] = [];

    readableStream.on('data', (data) => {
      const content: Buffer = data instanceof Buffer ? data : Buffer.from(data);
      chunks.push(content);
    });
    readableStream.on('end', () => {
      resolve(Buffer.concat(chunks));
    });
    readableStream.on('error', reject);
  });
}

If you're working with JavaScript in the browser, blob data returns in a promise blobBody. To learn more, see the example usage for browsers at BlobClient.download.

Resources

To learn more about how to download blobs using the Azure Blob Storage client library for JavaScript and TypeScript, see the following resources.

REST API operations

The Azure SDK for JavaScript and TypeScript contains libraries that build on top of the Azure REST API, allowing you to interact with REST API operations through familiar language paradigms. The client library methods for downloading blobs use the following REST API operation:

Code samples

View code samples from this article (GitHub):

Client library resources