Binary and text payloads
Representing request or response payloads with an explicit MIME type.
Node.js · Class
Blob
Blob encapsulates immutable raw data that can be safely shared across worker threads. It combines string or binary parts and supports byte, text, ArrayBuffer, and stream-based reads.
- Since
- v18.0.0
How it works
The global Blob class stores immutable raw data assembled from strings or binary parts. Its size and MIME type are available synchronously; arrayBuffer(), bytes(), text(), and stream() provide asynchronous or streaming access to the content, while the original data remains safely shareable across worker threads.
Syntax
new buffer.Blob([sources[, options]])Parameters
| Name | Type | Description |
|---|---|---|
sources | string[] | ArrayBuffer[] | TypedArray[] | DataView[] | Blob[] | Array of strings, ArrayBuffer, TypedArray, DataView, or Blob values to concatenate into the new Blob. |
options | Object | Optional settings. endings may be transparent or native; type specifies the content type. |
Returns
A Blob instance containing the concatenated source data.
Key points
- Blob represents immutable raw data suitable for safe sharing between worker threads.
- The constructor combines all supplied parts in order into one Blob.
- The size property reports the Blob's byte length.
- The type property exposes the configured MIME content type.
- bytes() asynchronously returns the content as a Uint8Array.
- stream() exposes Blob content through a ReadableStream.
Common mistakes
- String parts are encoded as UTF-8 and copied, so later changes to the original string source cannot affect the Blob.
- arrayBuffer() returns copied data rather than a view into the Blob's internal storage.
- Worker messaging can share a Blob without immediate transfer or copying; copying occurs when arrayBuffer() or text() is called.
Example: Create and read a Blob
const blob = new Blob(["hello", " world"], { type: "text/plain" });
console.log(blob.size, blob.type);
console.log(await blob.text());
const bytes = await blob.bytes();
console.log(bytes.length);Creates a text Blob, inspects its metadata, reads it as UTF-8 text, and obtains its bytes.
When to use it
Worker communication
Passing immutable data between worker threads through MessagePort.
Flexible data access
Reading content as bytes, UTF-8 text, an ArrayBuffer, or a stream.
Related
Blob.prototype.arrayBuffer()Blob.prototype.bytes()Blob.prototype.stream()Blob.prototype.text()MessagePort