Manage properties and metadata for a blob with JavaScript - Azure Storage (original) (raw)

In addition to the data they contain, blobs support system properties and user-defined metadata. This article shows how to manage system properties and user-defined metadata with the Azure Storage client library for JavaScript.

Prerequisites

Note

Blob index tags also provide the ability to store arbitrary user-defined key/value attributes alongside an Azure Blob storage resource. While similar to metadata, only blob index tags are automatically indexed and made searchable by the native blob service. Metadata cannot be indexed and queried unless you utilize a separate service such as Azure Search.

To learn more about this feature, see Manage and find data on Azure Blob storage with blob index (preview).

Set and retrieve properties

To set properties on a blob, use the following method:

The following code example sets the blobContentType and blobContentLanguage system properties on a blob.

Any properties not explicitly set are cleared. The following code example first gets the existing properties on the blob, then uses them to populate the headers that aren't being updated.

async function setHTTPHeaders(blobClient, headers) {
  
  // Get existing properties
  const properties = await blobClient.getProperties();

  // Set the blobContentType and blobContentLanguage headers
  // Populate the remaining headers from the existing properties
  blobHeaders = {
    blobContentType: 'text/plain',
    blobContentLanguage: 'en-us',
    blobContentEncoding: properties.contentEncoding,
    blobCacheControl: properties.cacheControl,
    blobContentDisposition: properties.contentDisposition,
    blobContentMD5: properties.contentMD5
  },

  await blobClient.setHTTPHeaders(blobHeaders);
}

To retrieve properties on a blob, use the following method:

The following code example gets a blob's system properties and displays some of the values:

async function getProperties(blobClient) {

  const properties = await blobClient.getProperties();
  
  console.log(`blobType: ${properties.blobType}`);
  console.log(`contentType: ${properties.contentType}`);
  console.log(`contentLength: ${properties.contentLength}`);
  console.log(`lastModified: ${properties.lastModified}`);
}

You can specify metadata as one or more name-value pairs on a blob or container resource. To set metadata, send a Metadata object containing name-value pairs using the following method:

The following code example sets metadata on a blob:

async function setBlobMetadata(blobClient, metadata) {
  
  metadata = {
    docType: 'text',
    category: 'reference'
  };

  await blobClient.setMetadata(metadata);
}

To retrieve metadata, call the getProperties method on your blob to populate the metadata collection, then read the values from the metadata property. The getProperties method retrieves blob properties and metadata by calling both the Get Blob Properties operation and the Get Blob Metadata operation.

Resources

To learn more about how to manage system properties and user-defined metadata using the Azure Blob Storage client library for JavaScript, see the following resources.

Code samples

REST API operations

The Azure SDK for JavaScript contains libraries that build on top of the Azure REST API, allowing you to interact with REST API operations through familiar JavaScript paradigms. The client library methods for managing system properties and user-defined metadata use the following REST API operations:

Client library resources

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