concat

BufferConstructor.concat

**concat**(list, totalLength?): [Buffer](/references/product/variables/Buffer-1)

Returns a new Buffer which is the result of concatenating all the Bufferinstances in the list together.

If the list has no items, or if the totalLength is 0, then a new zero-lengthBuffer is returned.

If totalLength is not provided, it is calculated from the Buffer instances in list by adding their lengths.

If totalLength is provided, it is coerced to an unsigned integer. If the combined length of the Buffers in list exceeds totalLength, the result is truncated to totalLength.

import { Buffer } from 'node:buffer';

// Create a single `Buffer` from a list of three `Buffer` instances.

const buf1 = Buffer.alloc(10);
const buf2 = Buffer.alloc(14);
const buf3 = Buffer.alloc(18);
const totalLength = buf1.length + buf2.length + buf3.length;

console.log(totalLength);
// Prints: 42

const bufA = Buffer.concat([buf1, buf2, buf3], totalLength);

console.log(bufA);
// Prints: <Buffer 00 00 00 00 ...>
console.log(bufA.length);
// Prints: 42

Buffer.concat() may also use the internal Buffer pool like Buffer.allocUnsafe() does.

Parameters

listreadonly Uint8Array[]Required

List of Buffer or Uint8Array instances to concatenate.

totalLengthnumber

Total length of the Buffer instances in list when concatenated.

Returns

Buffer

BufferBufferRequired

Since

v0.7.11