Class: Buffer#
The Buffer class is a global type for dealing with binary data directly.
It can be constructed in a variety of ways.
Static method: Buffer.alloc(size[, fill[, encoding]])#
Allocates a new Buffer of size bytes. If fill is undefined, the
Buffer will be zero-filled.
import { Buffer } from 'node:buffer';
const buf = Buffer.alloc(5);
console.log(buf);
const { Buffer } = require('node:buffer');
const buf = Buffer.alloc(5);
console.log(buf);
If size is larger than
buffer.constants.MAX_LENGTH or smaller than 0, ERR_OUT_OF_RANGE
is thrown.
If fill is specified, the allocated Buffer will be initialized by calling
buf.fill(fill).
import { Buffer } from 'node:buffer';
const buf = Buffer.alloc(5, 'a');
console.log(buf);
const { Buffer } = require('node:buffer');
const buf = Buffer.alloc(5, 'a');
console.log(buf);
If both fill and encoding are specified, the allocated Buffer will be
initialized by calling buf.fill(fill, encoding).
import { Buffer } from 'node:buffer';
const buf = Buffer.alloc(11, 'aGVsbG8gd29ybGQ=', 'base64');
console.log(buf);
const { Buffer } = require('node:buffer');
const buf = Buffer.alloc(11, 'aGVsbG8gd29ybGQ=', 'base64');
console.log(buf);
Calling Buffer.alloc() can be measurably slower than the alternative
Buffer.allocUnsafe() but ensures that the newly created Buffer instance
contents will never contain sensitive data from previous allocations, including
data that might not have been allocated for Buffers.
A TypeError will be thrown if size is not a number.
Static method: Buffer.allocUnsafe(size)#
Allocates a new Buffer of size bytes. If size is larger than
buffer.constants.MAX_LENGTH or smaller than 0, ERR_OUT_OF_RANGE
is thrown.
The underlying memory for Buffer instances created in this way is not
initialized. The contents of the newly created Buffer are unknown and
may contain sensitive data. Use Buffer.alloc() instead to initialize
Buffer instances with zeroes.
import { Buffer } from 'node:buffer';
const buf = Buffer.allocUnsafe(10);
console.log(buf);
buf.fill(0);
console.log(buf);
const { Buffer } = require('node:buffer');
const buf = Buffer.allocUnsafe(10);
console.log(buf);
buf.fill(0);
console.log(buf);
A TypeError will be thrown if size is not a number.
The Buffer module pre-allocates an internal Buffer instance of
size Buffer.poolSize that is used as a pool for the fast allocation of new
Buffer instances created using Buffer.allocUnsafe(), Buffer.from(array),
Buffer.from(string), and Buffer.concat() only when size is less than
Buffer.poolSize >>> 1 (floor of Buffer.poolSize divided by two).
Use of this pre-allocated internal memory pool is a key difference between
calling Buffer.alloc(size, fill) vs. Buffer.allocUnsafe(size).fill(fill).
Specifically, Buffer.alloc(size, fill) will never use the internal Buffer
pool, while Buffer.allocUnsafe(size).fill(fill) will use the internal
Buffer pool if size is less than or equal to half Buffer.poolSize. The
difference is subtle but can be important when an application requires the
additional performance that Buffer.allocUnsafe() provides.
Static method: Buffer.allocUnsafeSlow(size)#
Allocates a new Buffer of size bytes. If size is larger than
buffer.constants.MAX_LENGTH or smaller than 0, ERR_OUT_OF_RANGE
is thrown. A zero-length Buffer is created if size is 0.
The underlying memory for Buffer instances created in this way is not
initialized. The contents of the newly created Buffer are unknown and
may contain sensitive data. Use buf.fill(0) to initialize
such Buffer instances with zeroes.
When using Buffer.allocUnsafe() to allocate new Buffer instances,
allocations less than Buffer.poolSize >>> 1 (4KiB when default poolSize is used) are sliced
from a single pre-allocated Buffer. This allows applications to avoid the
garbage collection overhead of creating many individually allocated Buffer
instances. This approach improves both performance and memory usage by
eliminating the need to track and clean up as many individual ArrayBuffer objects.
However, in the case where a developer may need to retain a small chunk of
memory from a pool for an indeterminate amount of time, it may be appropriate
to create an un-pooled Buffer instance using Buffer.allocUnsafeSlow() and
then copying out the relevant bits.
import { Buffer } from 'node:buffer';
const store = [];
socket.on('readable', () => {
let data;
while (null !== (data = readable.read())) {
const sb = Buffer.allocUnsafeSlow(10);
data.copy(sb, 0, 0, 10);
store.push(sb);
}
});const { Buffer } = require('node:buffer');
const store = [];
socket.on('readable', () => {
let data;
while (null !== (data = readable.read())) {
const sb = Buffer.allocUnsafeSlow(10);
data.copy(sb, 0, 0, 10);
store.push(sb);
}
});
A TypeError will be thrown if size is not a number.
Static method: Buffer.byteLength(string[, encoding])#
Returns the byte length of a string when encoded using encoding.
This is not the same as String.prototype.length, which does not account
for the encoding that is used to convert the string into bytes.
For 'base64', 'base64url', and 'hex', this function assumes valid input.
For strings that contain non-base64/hex-encoded data (e.g. whitespace), the
return value might be greater than the length of a Buffer created from the
string.
import { Buffer } from 'node:buffer';
const str = '\u00bd + \u00bc = \u00be';
console.log(`${str}: ${str.length} characters, ` +
`${Buffer.byteLength(str, 'utf8')} bytes`);
const { Buffer } = require('node:buffer');
const str = '\u00bd + \u00bc = \u00be';
console.log(`${str}: ${str.length} characters, ` +
`${Buffer.byteLength(str, 'utf8')} bytes`);
When string is a <Buffer> | <DataView> | <TypedArray> | <ArrayBuffer> | <SharedArrayBuffer>,
the byte length as reported by .byteLength is returned.
Static method: Buffer.concat(list[, totalLength])#
Returns a new Buffer which is the result of concatenating all the Buffer
instances in the list together.
If the list has no items, or if the totalLength is 0, then a new zero-length
Buffer 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. If the combined length of the Buffers in list is
less than totalLength, the remaining space is filled with zeros.
import { Buffer } from 'node:buffer';
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);
const bufA = Buffer.concat([buf1, buf2, buf3], totalLength);
console.log(bufA);
console.log(bufA.length);
const { Buffer } = require('node:buffer');
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);
const bufA = Buffer.concat([buf1, buf2, buf3], totalLength);
console.log(bufA);
console.log(bufA.length);
Buffer.concat() may also use the internal Buffer pool like
Buffer.allocUnsafe() does.
Static method: Buffer.copyBytesFrom(view[, offset[, length]])#
Added in: v19.8.0, v18.16.0
Copies the underlying memory of view into a new Buffer.
const u16 = new Uint16Array([0, 0xffff]);
const buf = Buffer.copyBytesFrom(u16, 1, 1);
u16[1] = 0;
console.log(buf.length);
console.log(buf[0]);
console.log(buf[1]);
Static method: Buffer.from(array)#
Added in: v5.10.0
Allocates a new Buffer using an array of bytes in the range 0 – 255.
Array entries outside that range will be truncated to fit into it.
import { Buffer } from 'node:buffer';
const buf = Buffer.from([0x62, 0x75, 0x66, 0x66, 0x65, 0x72]);const { Buffer } = require('node:buffer');
const buf = Buffer.from([0x62, 0x75, 0x66, 0x66, 0x65, 0x72]);
If array is an Array-like object (that is, one with a length property of
type number), it is treated as if it is an array, unless it is a Buffer or
a Uint8Array. This means all other TypedArray variants get treated as an
Array. To create a Buffer from the bytes backing a TypedArray, use
Buffer.copyBytesFrom().
A TypeError will be thrown if array is not an Array or another type
appropriate for Buffer.from() variants.
Buffer.from(array) and Buffer.from(string) may also use the internal
Buffer pool like Buffer.allocUnsafe() does.
Static method: Buffer.from(arrayBuffer[, byteOffset[, length]])#
Added in: v5.10.0
This creates a view of the <ArrayBuffer> without copying the underlying
memory. For example, when passed a reference to the .buffer property of a
<TypedArray> instance, the newly created Buffer will share the same
allocated memory as the <TypedArray>'s underlying ArrayBuffer.
import { Buffer } from 'node:buffer';
const arr = new Uint16Array(2);
arr[0] = 5000;
arr[1] = 4000;
const buf = Buffer.from(arr.buffer);
console.log(buf);
arr[1] = 6000;
console.log(buf);
const { Buffer } = require('node:buffer');
const arr = new Uint16Array(2);
arr[0] = 5000;
arr[1] = 4000;
const buf = Buffer.from(arr.buffer);
console.log(buf);
arr[1] = 6000;
console.log(buf);
The optional byteOffset and length arguments specify a memory range within
the arrayBuffer that will be shared by the Buffer.
import { Buffer } from 'node:buffer';
const ab = new ArrayBuffer(10);
const buf = Buffer.from(ab, 0, 2);
console.log(buf.length);
const { Buffer } = require('node:buffer');
const ab = new ArrayBuffer(10);
const buf = Buffer.from(ab, 0, 2);
console.log(buf.length);
A TypeError will be thrown if arrayBuffer is not an <ArrayBuffer> or a
<SharedArrayBuffer> or another type appropriate for Buffer.from()
variants.
It is important to remember that a backing ArrayBuffer can cover a range
of memory that extends beyond the bounds of a TypedArray view. A new
Buffer created using the buffer property of a TypedArray may extend
beyond the range of the TypedArray:
import { Buffer } from 'node:buffer';
const arrA = Uint8Array.from([0x63, 0x64, 0x65, 0x66]);
const arrB = new Uint8Array(arrA.buffer, 1, 2);
console.log(arrA.buffer === arrB.buffer);
const buf = Buffer.from(arrB.buffer);
console.log(buf);
const { Buffer } = require('node:buffer');
const arrA = Uint8Array.from([0x63, 0x64, 0x65, 0x66]);
const arrB = new Uint8Array(arrA.buffer, 1, 2);
console.log(arrA.buffer === arrB.buffer);
const buf = Buffer.from(arrB.buffer);
console.log(buf);
Static method: Buffer.from(buffer)#
Added in: v5.10.0
Copies the passed buffer data onto a new Buffer instance.
import { Buffer } from 'node:buffer';
const buf1 = Buffer.from('buffer');
const buf2 = Buffer.from(buf1);
buf1[0] = 0x61;
console.log(buf1.toString());
console.log(buf2.toString());
const { Buffer } = require('node:buffer');
const buf1 = Buffer.from('buffer');
const buf2 = Buffer.from(buf1);
buf1[0] = 0x61;
console.log(buf1.toString());
console.log(buf2.toString());
A TypeError will be thrown if buffer is not a Buffer or another type
appropriate for Buffer.from() variants.
Static method: Buffer.from(string[, encoding])#
Added in: v5.10.0
Creates a new Buffer containing string. The encoding parameter identifies
the character encoding to be used when converting string into bytes.
import { Buffer } from 'node:buffer';
const buf1 = Buffer.from('this is a tést');
const buf2 = Buffer.from('7468697320697320612074c3a97374', 'hex');
console.log(buf1.toString());
console.log(buf2.toString());
console.log(buf1.toString('latin1'));
const { Buffer } = require('node:buffer');
const buf1 = Buffer.from('this is a tést');
const buf2 = Buffer.from('7468697320697320612074c3a97374', 'hex');
console.log(buf1.toString());
console.log(buf2.toString());
console.log(buf1.toString('latin1'));
A TypeError will be thrown if string is not a string or another type
appropriate for Buffer.from() variants.
Buffer.from(string) may also use the internal Buffer pool like
Buffer.allocUnsafe() does.
Buffer.poolSize#
Added in: v0.11.3
This is the size (in bytes) of pre-allocated internal Buffer instances used
for pooling. This value may be modified.
buf.byteOffset#
- Type: <integer> The
byteOffset of the Buffer's underlying ArrayBuffer object.
When setting byteOffset in Buffer.from(ArrayBuffer, byteOffset, length),
or sometimes when allocating a Buffer smaller than Buffer.poolSize, the
buffer does not start from a zero offset on the underlying ArrayBuffer.
This can cause problems when accessing the underlying ArrayBuffer directly
using buf.buffer, as other parts of the ArrayBuffer may be unrelated
to the Buffer object itself.
A common issue when creating a TypedArray object that shares its memory with
a Buffer is that in this case one needs to specify the byteOffset correctly:
import { Buffer } from 'node:buffer';
const nodeBuffer = Buffer.from([0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
new Int8Array(nodeBuffer.buffer, nodeBuffer.byteOffset, nodeBuffer.length);const { Buffer } = require('node:buffer');
const nodeBuffer = Buffer.from([0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
new Int8Array(nodeBuffer.buffer, nodeBuffer.byteOffset, nodeBuffer.length);
buf.compare(target[, targetStart[, targetEnd[, sourceStart[, sourceEnd]]]])#
target <Buffer> | <Uint8Array> A Buffer or <Uint8Array> with which to
compare buf.
targetStart <integer> The offset within target at which to begin
comparison. Default: 0.
targetEnd <integer> The offset within target at which to end comparison
(not inclusive). Default: target.length.
sourceStart <integer> The offset within buf at which to begin comparison.
Default: 0.
sourceEnd <integer> The offset within buf at which to end comparison
(not inclusive). Default: buf.length.
- Returns: <integer>
Compares buf with target and returns a number indicating whether buf
comes before, after, or is the same as target in sort order.
Comparison is based on the actual sequence of bytes in each Buffer.
0 is returned if target is the same as buf
1 is returned if target should come before buf when sorted.
-1 is returned if target should come after buf when sorted.
import { Buffer } from 'node:buffer';
const buf1 = Buffer.from('ABC');
const buf2 = Buffer.from('BCD');
const buf3 = Buffer.from('ABCD');
console.log(buf1.compare(buf1));
console.log(buf1.compare(buf2));
console.log(buf1.compare(buf3));
console.log(buf2.compare(buf1));
console.log(buf2.compare(buf3));
console.log([buf1, buf2, buf3].sort(Buffer.compare));
const { Buffer } = require('node:buffer');
const buf1 = Buffer.from('ABC');
const buf2 = Buffer.from('BCD');
const buf3 = Buffer.from('ABCD');
console.log(buf1.compare(buf1));
console.log(buf1.compare(buf2));
console.log(buf1.compare(buf3));
console.log(buf2.compare(buf1));
console.log(buf2.compare(buf3));
console.log([buf1, buf2, buf3].sort(Buffer.compare));
The optional targetStart, targetEnd, sourceStart, and sourceEnd
arguments can be used to limit the comparison to specific ranges within target
and buf respectively.
import { Buffer } from 'node:buffer';
const buf1 = Buffer.from([1, 2, 3, 4, 5, 6, 7, 8, 9]);
const buf2 = Buffer.from([5, 6, 7, 8, 9, 1, 2, 3, 4]);
console.log(buf1.compare(buf2, 5, 9, 0, 4));
console.log(buf1.compare(buf2, 0, 6, 4));
console.log(buf1.compare(buf2, 5, 6, 5));
const { Buffer } = require('node:buffer');
const buf1 = Buffer.from([1, 2, 3, 4, 5, 6, 7, 8, 9]);
const buf2 = Buffer.from([5, 6, 7, 8, 9, 1, 2, 3, 4]);
console.log(buf1.compare(buf2, 5, 9, 0, 4));
console.log(buf1.compare(buf2, 0, 6, 4));
console.log(buf1.compare(buf2, 5, 6, 5));
ERR_OUT_OF_RANGE is thrown if targetStart < 0, sourceStart < 0,
targetEnd > target.byteLength, or sourceEnd > source.byteLength.
buf.copy(target[, targetStart[, sourceStart[, sourceEnd]]])#
Added in: v0.1.90
target <Buffer> | <Uint8Array> A Buffer or <Uint8Array> to copy into.
targetStart <integer> The offset within target at which to begin
writing. Default: 0.
sourceStart <integer> The offset within buf from which to begin copying.
Default: 0.
sourceEnd <integer> The offset within buf at which to stop copying (not
inclusive). Default: buf.length.
- Returns: <integer> The number of bytes copied.
Copies data from a region of buf to a region in target, even if the target
memory region overlaps with buf.
TypedArray.prototype.set() performs the same operation, and is available
for all TypedArrays, including Node.js Buffers, although it takes
different function arguments.
import { Buffer } from 'node:buffer';
const buf1 = Buffer.allocUnsafe(26);
const buf2 = Buffer.allocUnsafe(26).fill('!');
for (let i = 0; i < 26; i++) {
buf1[i] = i + 97;
}
buf1.copy(buf2, 8, 16, 20);
console.log(buf2.toString('ascii', 0, 25));
const { Buffer } = require('node:buffer');
const buf1 = Buffer.allocUnsafe(26);
const buf2 = Buffer.allocUnsafe(26).fill('!');
for (let i = 0; i < 26; i++) {
buf1[i] = i + 97;
}
buf1.copy(buf2, 8, 16, 20);
console.log(buf2.toString('ascii', 0, 25));
import { Buffer } from 'node:buffer';
const buf = Buffer.allocUnsafe(26);
for (let i = 0; i < 26; i++) {
buf[i] = i + 97;
}
buf.copy(buf, 0, 4, 10);
console.log(buf.toString());
const { Buffer } = require('node:buffer');
const buf = Buffer.allocUnsafe(26);
for (let i = 0; i < 26; i++) {
buf[i] = i + 97;
}
buf.copy(buf, 0, 4, 10);
console.log(buf.toString());
buf.fill(value[, offset[, end]][, encoding])#
value <string> | <Buffer> | <Uint8Array> | <integer> The value with which to fill buf.
Empty value (string, Uint8Array, Buffer) is coerced to 0.
offset <integer> Number of bytes to skip before starting to fill buf.
Default: 0.
end <integer> Where to stop filling buf (not inclusive). Default:
buf.length.
encoding <string> The encoding for value if value is a string.
Default: 'utf8'.
- Returns: <Buffer> A reference to
buf.
Fills buf with the specified value. If the offset and end are not given,
the entire buf will be filled:
import { Buffer } from 'node:buffer';
const b = Buffer.allocUnsafe(50).fill('h');
console.log(b.toString());
const c = Buffer.allocUnsafe(5).fill('');
console.log(c.fill(''));
const { Buffer } = require('node:buffer');
const b = Buffer.allocUnsafe(50).fill('h');
console.log(b.toString());
const c = Buffer.allocUnsafe(5).fill('');
console.log(c.fill(''));
value is coerced to a uint32 value if it is not a string, Buffer, or
integer. If the resulting integer is greater than 255 (decimal), buf will be
filled with value & 255.
If the final write of a fill() operation falls on a multi-byte character,
then only the bytes of that character that fit into buf are written:
import { Buffer } from 'node:buffer';
console.log(Buffer.allocUnsafe(5).fill('\u0222'));
const { Buffer } = require('node:buffer');
console.log(Buffer.allocUnsafe(5).fill('\u0222'));
If value contains invalid characters, it is truncated; if no valid
fill data remains, an exception is thrown:
import { Buffer } from 'node:buffer';
const buf = Buffer.allocUnsafe(5);
console.log(buf.fill('a'));
console.log(buf.fill('aazz', 'hex'));
console.log(buf.fill('zz', 'hex'));
const { Buffer } = require('node:buffer');
const buf = Buffer.allocUnsafe(5);
console.log(buf.fill('a'));
console.log(buf.fill('aazz', 'hex'));
console.log(buf.fill('zz', 'hex'));
buf.indexOf(value[, byteOffset][, encoding])#
value <string> | <Buffer> | <Uint8Array> | <integer> What to search for.
byteOffset <integer> Where to begin searching in buf. If negative, then
offset is calculated from the end of buf. Default: 0.
encoding <string> If value is a string, this is the encoding used to
determine the binary representation of the string that will be searched for in
buf. Default: 'utf8'.
- Returns: <integer> The index of the first occurrence of
value in buf, or
-1 if buf does not contain value.
If value is:
- a string,
value is interpreted according to the character encoding in
encoding.
- a
Buffer or <Uint8Array>, value will be used in its entirety.
To compare a partial Buffer, use buf.subarray.
- a number,
value will be interpreted as an unsigned 8-bit integer
value between 0 and 255.
import { Buffer } from 'node:buffer';
const buf = Buffer.from('this is a buffer');
console.log(buf.indexOf('this'));
console.log(buf.indexOf('is'));
console.log(buf.indexOf(Buffer.from('a buffer')));
console.log(buf.indexOf(97));
console.log(buf.indexOf(Buffer.from('a buffer example')));
console.log(buf.indexOf(Buffer.from('a buffer example').slice(0, 8)));
const utf16Buffer = Buffer.from('\u039a\u0391\u03a3\u03a3\u0395', 'utf16le');
console.log(utf16Buffer.indexOf('\u03a3', 0, 'utf16le'));
console.log(utf16Buffer.indexOf('\u03a3', -4, 'utf16le'));
const { Buffer } = require('node:buffer');
const buf = Buffer.from('this is a buffer');
console.log(buf.indexOf('this'));
console.log(buf.indexOf('is'));
console.log(buf.indexOf(Buffer.from('a buffer')));
console.log(buf.indexOf(97));
console.log(buf.indexOf(Buffer.from('a buffer example')));
console.log(buf.indexOf(Buffer.from('a buffer example').slice(0, 8)));
const utf16Buffer = Buffer.from('\u039a\u0391\u03a3\u03a3\u0395', 'utf16le');
console.log(utf16Buffer.indexOf('\u03a3', 0, 'utf16le'));
console.log(utf16Buffer.indexOf('\u03a3', -4, 'utf16le'));
If value is not a string, number, or Buffer, this method will throw a
TypeError. If value is a number, it will be coerced to a valid byte value,
an integer between 0 and 255.
If byteOffset is not a number, it will be coerced to a number. If the result
of coercion is NaN or 0, then the entire buffer will be searched. This
behavior matches String.prototype.indexOf().
import { Buffer } from 'node:buffer';
const b = Buffer.from('abcdef');
console.log(b.indexOf(99.9));
console.log(b.indexOf(256 + 99));
console.log(b.indexOf('b', undefined));
console.log(b.indexOf('b', {}));
console.log(b.indexOf('b', null));
console.log(b.indexOf('b', []));const { Buffer } = require('node:buffer');
const b = Buffer.from('abcdef');
console.log(b.indexOf(99.9));
console.log(b.indexOf(256 + 99));
console.log(b.indexOf('b', undefined));
console.log(b.indexOf('b', {}));
console.log(b.indexOf('b', null));
console.log(b.indexOf('b', []));
If value is an empty string or empty Buffer and byteOffset is less
than buf.length, byteOffset will be returned. If value is empty and
byteOffset is at least buf.length, buf.length will be returned.
buf.lastIndexOf(value[, byteOffset][, encoding])#
value <string> | <Buffer> | <Uint8Array> | <integer> What to search for.
byteOffset <integer> Where to begin searching in buf. If negative, then
offset is calculated from the end of buf. Default:
buf.length - 1.
encoding <string> If value is a string, this is the encoding used to
determine the binary representation of the string that will be searched for in
buf. Default: 'utf8'.
- Returns: <integer> The index of the last occurrence of
value in buf, or
-1 if buf does not contain value.
Identical to buf.indexOf(), except the last occurrence of value is found
rather than the first occurrence.
import { Buffer } from 'node:buffer';
const buf = Buffer.from('this buffer is a buffer');
console.log(buf.lastIndexOf('this'));
console.log(buf.lastIndexOf('buffer'));
console.log(buf.lastIndexOf(Buffer.from('buffer')));
console.log(buf.lastIndexOf(97));
console.log(buf.lastIndexOf(Buffer.from('yolo')));
console.log(buf.lastIndexOf('buffer', 5));
console.log(buf.lastIndexOf('buffer', 4));
const utf16Buffer = Buffer.from('\u039a\u0391\u03a3\u03a3\u0395', 'utf16le');
console.log(utf16Buffer.lastIndexOf('\u03a3', undefined, 'utf16le'));
console.log(utf16Buffer.lastIndexOf('\u03a3', -5, 'utf16le'));
const { Buffer } = require('node:buffer');
const buf = Buffer.from('this buffer is a buffer');
console.log(buf.lastIndexOf('this'));
console.log(buf.lastIndexOf('buffer'));
console.log(buf.lastIndexOf(Buffer.from('buffer')));
console.log(buf.lastIndexOf(97));
console.log(buf.lastIndexOf(Buffer.from('yolo')));
console.log(buf.lastIndexOf('buffer', 5));
console.log(buf.lastIndexOf('buffer', 4));
const utf16Buffer = Buffer.from('\u039a\u0391\u03a3\u03a3\u0395', 'utf16le');
console.log(utf16Buffer.lastIndexOf('\u03a3', undefined, 'utf16le'));
console.log(utf16Buffer.lastIndexOf('\u03a3', -5, 'utf16le'));
If value is not a string, number, or Buffer, this method will throw a
TypeError. If value is a number, it will be coerced to a valid byte value,
an integer between 0 and 255.
If byteOffset is not a number, it will be coerced to a number. Any arguments
that coerce to NaN, like {} or undefined, will search the whole buffer.
This behavior matches String.prototype.lastIndexOf().
import { Buffer } from 'node:buffer';
const b = Buffer.from('abcdef');
console.log(b.lastIndexOf(99.9));
console.log(b.lastIndexOf(256 + 99));
console.log(b.lastIndexOf('b', undefined));
console.log(b.lastIndexOf('b', {}));
console.log(b.lastIndexOf('b', null));
console.log(b.lastIndexOf('b', []));const { Buffer } = require('node:buffer');
const b = Buffer.from('abcdef');
console.log(b.lastIndexOf(99.9));
console.log(b.lastIndexOf(256 + 99));
console.log(b.lastIndexOf('b', undefined));
console.log(b.lastIndexOf('b', {}));
console.log(b.lastIndexOf('b', null));
console.log(b.lastIndexOf('b', []));
If value is an empty string or empty Buffer, byteOffset will be returned.
buf.parent#
Deprecated since: v8.0.0
The buf.parent property is a deprecated alias for buf.buffer.
buf.readBigInt64BE([offset])#
Added in: v12.0.0, v10.20.0
offset <integer> Number of bytes to skip before starting to read. Must
satisfy: 0 <= offset <= buf.length - 8. Default: 0.
- Returns: <bigint>
Reads a signed, big-endian 64-bit integer from buf at the specified offset.
Integers read from a Buffer are interpreted as two's complement signed
values.
buf.readBigInt64LE([offset])#
Added in: v12.0.0, v10.20.0
offset <integer> Number of bytes to skip before starting to read. Must
satisfy: 0 <= offset <= buf.length - 8. Default: 0.
- Returns: <bigint>
Reads a signed, little-endian 64-bit integer from buf at the specified
offset.
Integers read from a Buffer are interpreted as two's complement signed
values.
buf.readBigUInt64BE([offset])#
offset <integer> Number of bytes to skip before starting to read. Must
satisfy: 0 <= offset <= buf.length - 8. Default: 0.
- Returns: <bigint>
Reads an unsigned, big-endian 64-bit integer from buf at the specified
offset.
This function is also available under the readBigUint64BE alias.
import { Buffer } from 'node:buffer';
const buf = Buffer.from([0x00, 0x00, 0x00, 0x00, 0xff, 0xff, 0xff, 0xff]);
console.log(buf.readBigUInt64BE(0));
const { Buffer } = require('node:buffer');
const buf = Buffer.from([0x00, 0x00, 0x00, 0x00, 0xff, 0xff, 0xff, 0xff]);
console.log(buf.readBigUInt64BE(0));
buf.readBigUInt64LE([offset])#
offset <integer> Number of bytes to skip before starting to read. Must
satisfy: 0 <= offset <= buf.length - 8. Default: 0.
- Returns: <bigint>
Reads an unsigned, little-endian 64-bit integer from buf at the specified
offset.
This function is also available under the readBigUint64LE alias.
import { Buffer } from 'node:buffer';
const buf = Buffer.from([0x00, 0x00, 0x00, 0x00, 0xff, 0xff, 0xff, 0xff]);
console.log(buf.readBigUInt64LE(0));
const { Buffer } = require('node:buffer');
const buf = Buffer.from([0x00, 0x00, 0x00, 0x00, 0xff, 0xff, 0xff, 0xff]);
console.log(buf.readBigUInt64LE(0));
buf.readDoubleBE([offset])#
offset <integer> Number of bytes to skip before starting to read. Must
satisfy 0 <= offset <= buf.length - 8. Default: 0.
- Returns: <number>
Reads a 64-bit, big-endian double from buf at the specified offset.
import { Buffer } from 'node:buffer';
const buf = Buffer.from([1, 2, 3, 4, 5, 6, 7, 8]);
console.log(buf.readDoubleBE(0));
const { Buffer } = require('node:buffer');
const buf = Buffer.from([1, 2, 3, 4, 5, 6, 7, 8]);
console.log(buf.readDoubleBE(0));
buf.readDoubleLE([offset])#
offset <integer> Number of bytes to skip before starting to read. Must
satisfy 0 <= offset <= buf.length - 8. Default: 0.
- Returns: <number>
Reads a 64-bit, little-endian double from buf at the specified offset.
import { Buffer } from 'node:buffer';
const buf = Buffer.from([1, 2, 3, 4, 5, 6, 7, 8]);
console.log(buf.readDoubleLE(0));
console.log(buf.readDoubleLE(1));
const { Buffer } = require('node:buffer');
const buf = Buffer.from([1, 2, 3, 4, 5, 6, 7, 8]);
console.log(buf.readDoubleLE(0));
console.log(buf.readDoubleLE(1));
buf.readIntBE(offset, byteLength)#
offset <integer> Number of bytes to skip before starting to read. Must
satisfy 0 <= offset <= buf.length - byteLength.
byteLength <integer> Number of bytes to read. Must satisfy
0 < byteLength <= 6.
- Returns: <integer>
Reads byteLength number of bytes from buf at the specified offset
and interprets the result as a big-endian, two's complement signed value
supporting up to 48 bits of accuracy.
import { Buffer } from 'node:buffer';
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);
console.log(buf.readIntBE(0, 6).toString(16));
console.log(buf.readIntBE(1, 6).toString(16));
console.log(buf.readIntBE(1, 0).toString(16));
const { Buffer } = require('node:buffer');
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);
console.log(buf.readIntBE(0, 6).toString(16));
console.log(buf.readIntBE(1, 6).toString(16));
console.log(buf.readIntBE(1, 0).toString(16));
buf.readIntLE(offset, byteLength)#
offset <integer> Number of bytes to skip before starting to read. Must
satisfy 0 <= offset <= buf.length - byteLength.
byteLength <integer> Number of bytes to read. Must satisfy
0 < byteLength <= 6.
- Returns: <integer>
Reads byteLength number of bytes from buf at the specified offset
and interprets the result as a little-endian, two's complement signed value
supporting up to 48 bits of accuracy.
import { Buffer } from 'node:buffer';
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);
console.log(buf.readIntLE(0, 6).toString(16));
const { Buffer } = require('node:buffer');
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);
console.log(buf.readIntLE(0, 6).toString(16));
buf.readUIntBE(offset, byteLength)#
offset <integer> Number of bytes to skip before starting to read. Must
satisfy 0 <= offset <= buf.length - byteLength.
byteLength <integer> Number of bytes to read. Must satisfy
0 < byteLength <= 6.
- Returns: <integer>
Reads byteLength number of bytes from buf at the specified offset
and interprets the result as an unsigned big-endian integer supporting
up to 48 bits of accuracy.
This function is also available under the readUintBE alias.
import { Buffer } from 'node:buffer';
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);
console.log(buf.readUIntBE(0, 6).toString(16));
console.log(buf.readUIntBE(1, 6).toString(16));
const { Buffer } = require('node:buffer');
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);
console.log(buf.readUIntBE(0, 6).toString(16));
console.log(buf.readUIntBE(1, 6).toString(16));
buf.readUIntLE(offset, byteLength)#
offset <integer> Number of bytes to skip before starting to read. Must
satisfy 0 <= offset <= buf.length - byteLength.
byteLength <integer> Number of bytes to read. Must satisfy
0 < byteLength <= 6.
- Returns: <integer>
Reads byteLength number of bytes from buf at the specified offset
and interprets the result as an unsigned, little-endian integer supporting
up to 48 bits of accuracy.
This function is also available under the readUintLE alias.
import { Buffer } from 'node:buffer';
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);
console.log(buf.readUIntLE(0, 6).toString(16));
const { Buffer } = require('node:buffer');
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);
console.log(buf.readUIntLE(0, 6).toString(16));
buf.subarray([start[, end]])#
Added in: v3.0.0
Returns a new Buffer that references the same memory as the original, but
offset and cropped by the start and end indexes.
Specifying end greater than buf.length will return the same result as
that of end equal to buf.length.
This method is inherited from TypedArray.prototype.subarray().
Modifying the new Buffer slice will modify the memory in the original Buffer
because the allocated memory of the two objects overlap.
import { Buffer } from 'node:buffer';
const buf1 = Buffer.allocUnsafe(26);
for (let i = 0; i < 26; i++) {
buf1[i] = i + 97;
}
const buf2 = buf1.subarray(0, 3);
console.log(buf2.toString('ascii', 0, buf2.length));
buf1[0] = 33;
console.log(buf2.toString('ascii', 0, buf2.length));
const { Buffer } = require('node:buffer');
const buf1 = Buffer.allocUnsafe(26);
for (let i = 0; i < 26; i++) {
buf1[i] = i + 97;
}
const buf2 = buf1.subarray(0, 3);
console.log(buf2.toString('ascii', 0, buf2.length));
buf1[0] = 33;
console.log(buf2.toString('ascii', 0, buf2.length));
Specifying negative indexes causes the slice to be generated relative to the
end of buf rather than the beginning.
import { Buffer } from 'node:buffer';
const buf = Buffer.from('buffer');
console.log(buf.subarray(-6, -1).toString());
console.log(buf.subarray(-6, -2).toString());
console.log(buf.subarray(-5, -2).toString());
const { Buffer } = require('node:buffer');
const buf = Buffer.from('buffer');
console.log(buf.subarray(-6, -1).toString());
console.log(buf.subarray(-6, -2).toString());
console.log(buf.subarray(-5, -2).toString());
buf.slice([start[, end]])#
Returns a new Buffer that references the same memory as the original, but
offset and cropped by the start and end indexes.
This method is not compatible with the Uint8Array.prototype.slice(),
which is a superclass of Buffer. To copy the slice, use
Uint8Array.prototype.slice().
import { Buffer } from 'node:buffer';
const buf = Buffer.from('buffer');
const copiedBuf = Uint8Array.prototype.slice.call(buf);
copiedBuf[0]++;
console.log(copiedBuf.toString());
console.log(buf.toString());
const notReallyCopiedBuf = buf.slice();
notReallyCopiedBuf[0]++;
console.log(notReallyCopiedBuf.toString());
console.log(buf.toString());
const { Buffer } = require('node:buffer');
const buf = Buffer.from('buffer');
const copiedBuf = Uint8Array.prototype.slice.call(buf);
copiedBuf[0]++;
console.log(copiedBuf.toString());
console.log(buf.toString());
const notReallyCopiedBuf = buf.slice();
notReallyCopiedBuf[0]++;
console.log(notReallyCopiedBuf.toString());
console.log(buf.toString());
buf.swap16()#
Added in: v5.10.0
Interprets buf as an array of unsigned 16-bit integers and swaps the
byte order in-place. Throws ERR_INVALID_BUFFER_SIZE if buf.length
is not a multiple of 2.
import { Buffer } from 'node:buffer';
const buf1 = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8]);
console.log(buf1);
buf1.swap16();
console.log(buf1);
const buf2 = Buffer.from([0x1, 0x2, 0x3]);
buf2.swap16();
const { Buffer } = require('node:buffer');
const buf1 = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8]);
console.log(buf1);
buf1.swap16();
console.log(buf1);
const buf2 = Buffer.from([0x1, 0x2, 0x3]);
buf2.swap16();
One convenient use of buf.swap16() is to perform a fast in-place conversion
between UTF-16 little-endian and UTF-16 big-endian:
import { Buffer } from 'node:buffer';
const buf = Buffer.from('This is little-endian UTF-16', 'utf16le');
buf.swap16(); const { Buffer } = require('node:buffer');
const buf = Buffer.from('This is little-endian UTF-16', 'utf16le');
buf.swap16();
buf.swap32()#
Added in: v5.10.0
Interprets buf as an array of unsigned 32-bit integers and swaps the
byte order in-place. Throws ERR_INVALID_BUFFER_SIZE if buf.length
is not a multiple of 4.
import { Buffer } from 'node:buffer';
const buf1 = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8]);
console.log(buf1);
buf1.swap32();
console.log(buf1);
const buf2 = Buffer.from([0x1, 0x2, 0x3]);
buf2.swap32();
const { Buffer } = require('node:buffer');
const buf1 = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8]);
console.log(buf1);
buf1.swap32();
console.log(buf1);
const buf2 = Buffer.from([0x1, 0x2, 0x3]);
buf2.swap32();
buf.swap64()#
Added in: v6.3.0
Interprets buf as an array of 64-bit numbers and swaps byte order in-place.
Throws ERR_INVALID_BUFFER_SIZE if buf.length is not a multiple of 8.
import { Buffer } from 'node:buffer';
const buf1 = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8]);
console.log(buf1);
buf1.swap64();
console.log(buf1);
const buf2 = Buffer.from([0x1, 0x2, 0x3]);
buf2.swap64();
const { Buffer } = require('node:buffer');
const buf1 = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8]);
console.log(buf1);
buf1.swap64();
console.log(buf1);
const buf2 = Buffer.from([0x1, 0x2, 0x3]);
buf2.swap64();
buf.toJSON()#
Added in: v0.9.2
Returns a JSON representation of buf. JSON.stringify() implicitly calls
this function when stringifying a Buffer instance.
Buffer.from() accepts objects in the format returned from this method.
In particular, Buffer.from(buf.toJSON()) works like Buffer.from(buf).
import { Buffer } from 'node:buffer';
const buf = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5]);
const json = JSON.stringify(buf);
console.log(json);
const copy = JSON.parse(json, (key, value) => {
return value && value.type === 'Buffer' ?
Buffer.from(value) :
value;
});
console.log(copy);
const { Buffer } = require('node:buffer');
const buf = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5]);
const json = JSON.stringify(buf);
console.log(json);
const copy = JSON.parse(json, (key, value) => {
return value && value.type === 'Buffer' ?
Buffer.from(value) :
value;
});
console.log(copy);
buf.toString([encoding[, start[, end]]])#
Added in: v0.1.90
encoding <string> The character encoding to use. Default: 'utf8'.
start <integer> The byte offset to start decoding at. Default: 0.
end <integer> The byte offset to stop decoding at (not inclusive).
Default: buf.length.
- Returns: <string>
Decodes buf to a string according to the specified character encoding in
encoding. start and end may be passed to decode only a subset of buf.
If encoding is 'utf8' and a byte sequence in the input is not valid UTF-8,
then each invalid byte is replaced with the replacement character U+FFFD.
The maximum length of a string instance (in UTF-16 code units) is available
as buffer.constants.MAX_STRING_LENGTH.
import { Buffer } from 'node:buffer';
const buf1 = Buffer.allocUnsafe(26);
for (let i = 0; i < 26; i++) {
buf1[i] = i + 97;
}
console.log(buf1.toString('utf8'));
console.log(buf1.toString('utf8', 0, 5));
const buf2 = Buffer.from('tést');
console.log(buf2.toString('hex'));
console.log(buf2.toString('utf8', 0, 3));
console.log(buf2.toString(undefined, 0, 3));
const { Buffer } = require('node:buffer');
const buf1 = Buffer.allocUnsafe(26);
for (let i = 0; i < 26; i++) {
buf1[i] = i + 97;
}
console.log(buf1.toString('utf8'));
console.log(buf1.toString('utf8', 0, 5));
const buf2 = Buffer.from('tést');
console.log(buf2.toString('hex'));
console.log(buf2.toString('utf8', 0, 3));
console.log(buf2.toString(undefined, 0, 3));
buf.write(string[, offset[, length]][, encoding])#
Added in: v0.1.90
string <string> String to write to buf.
offset <integer> Number of bytes to skip before starting to write string.
Default: 0.
length <integer> Maximum number of bytes to write (written bytes will not
exceed buf.length - offset). Default: buf.length - offset.
encoding <string> The character encoding of string. Default: 'utf8'.
- Returns: <integer> Number of bytes written.
Writes string to buf at offset according to the character encoding in
encoding. The length parameter is the number of bytes to write. If buf did
not contain enough space to fit the entire string, only part of string will be
written. However, partially encoded characters will not be written.
import { Buffer } from 'node:buffer';
const buf = Buffer.alloc(256);
const len = buf.write('\u00bd + \u00bc = \u00be', 0);
console.log(`${len} bytes: ${buf.toString('utf8', 0, len)}`);
const buffer = Buffer.alloc(10);
const length = buffer.write('abcd', 8);
console.log(`${length} bytes: ${buffer.toString('utf8', 8, 10)}`);
const { Buffer } = require('node:buffer');
const buf = Buffer.alloc(256);
const len = buf.write('\u00bd + \u00bc = \u00be', 0);
console.log(`${len} bytes: ${buf.toString('utf8', 0, len)}`);
const buffer = Buffer.alloc(10);
const length = buffer.write('abcd', 8);
console.log(`${length} bytes: ${buffer.toString('utf8', 8, 10)}`);
buf.writeBigInt64BE(value[, offset])#
Added in: v12.0.0, v10.20.0
value <bigint> Number to be written to buf.
offset <integer> Number of bytes to skip before starting to write. Must
satisfy: 0 <= offset <= buf.length - 8. Default: 0.
- Returns: <integer>
offset plus the number of bytes written.
Writes value to buf at the specified offset as big-endian.
value is interpreted and written as a two's complement signed integer.
import { Buffer } from 'node:buffer';
const buf = Buffer.allocUnsafe(8);
buf.writeBigInt64BE(0x0102030405060708n, 0);
console.log(buf);
const { Buffer } = require('node:buffer');
const buf = Buffer.allocUnsafe(8);
buf.writeBigInt64BE(0x0102030405060708n, 0);
console.log(buf);
buf.writeBigInt64LE(value[, offset])#
Added in: v12.0.0, v10.20.0
value <bigint> Number to be written to buf.
offset <integer> Number of bytes to skip before starting to write. Must
satisfy: 0 <= offset <= buf.length - 8. Default: 0.
- Returns: <integer>
offset plus the number of bytes written.
Writes value to buf at the specified offset as little-endian.
value is interpreted and written as a two's complement signed integer.
import { Buffer } from 'node:buffer';
const buf = Buffer.allocUnsafe(8);
buf.writeBigInt64LE(0x0102030405060708n, 0);
console.log(buf);
const { Buffer } = require('node:buffer');
const buf = Buffer.allocUnsafe(8);
buf.writeBigInt64LE(0x0102030405060708n, 0);
console.log(buf);