Convert a Buffer (node:buffer)

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Node.js APIs and many npm packages produce Buffer objects. Deno supports Buffer through the node:buffer module, and since Buffer is a subclass of Uint8Array, converting to web-standard types is straightforward. This example shows the common conversions in both directions.

import { Buffer } from "node:buffer";

We start with a Buffer containing the bytes of the string "Hello".

const buffer = Buffer.from("Hello", "utf8");

To convert to a string, use the built-in toString method with an optional encoding.

console.log(buffer.toString("utf8")); // Hello

A Buffer is a subclass of Uint8Array, so web APIs accept it directly. To get a plain Uint8Array view over the same memory, pass byteOffset and length. Buffers are often slices of a larger shared allocation.

const bytes = new Uint8Array(buffer.buffer, buffer.byteOffset, buffer.length);
console.log(bytes); // Uint8Array(5) [ 72, 101, 108, 108, 111 ]

To get an exact ArrayBuffer, slice the range out of the underlying buffer. Taking the buffer property alone may include unrelated bytes from the shared allocation pool.

const arrayBuffer = buffer.buffer.slice(
  buffer.byteOffset,
  buffer.byteOffset + buffer.byteLength,
);
console.log(arrayBuffer.byteLength); // 5

The Blob constructor accepts a Buffer like any other view.

const blob = new Blob([buffer]);
console.log(blob.size); // 5

To convert to a ReadableStream, wrap it with ReadableStream.from.

const stream = ReadableStream.from([buffer]);
console.log(stream instanceof ReadableStream); // true

For the reverse direction, TextDecoder accepts any ArrayBuffer view, so it decodes DataViews and Buffers directly.

const view = new DataView(arrayBuffer);
console.log(new TextDecoder().decode(view)); // Hello

Run this example locally using the Deno CLI:

deno run https://docs.deno.com/examples/scripts/convert_buffer.ts

Convert a Buffer (node:buffer)

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