ArrayBuffer and DataView Fundamentals

JavaScript exposes raw binary storage through the ArrayBuffer object, a fixed-length byte buffer whose cnotents cannot be accessed dircetly. To read or write data, wrap the buffer in a view such as DataView, which offers low-level, endian-aware methods for all common numeric types.

const buf = new ArrayBuffer(8);      // 8-byte buffer
const view = new DataView(buf);      // endian-agnostic accessor

Endianness

Multi-byte values can be stored in little-endian (least-significant byte first) or big-endian (most-significant byte first) order. DataView lets you choose explicitly:

view.setInt32(0, 0x12345678, true);  // little-endian
view.setInt32(0, 0x12345678, false); // big-endian (default)

Encoding 16- and 32-bit Integers

Store a 16-bit signed integer followed by a 32-bit signed integer in a 6-byte buffer:

const bytes = new ArrayBuffer(6);
const dv = new DataView(bytes);

dv.setInt16(0, 3000);      // offset 0, value 3000
dv.setInt32(2, 987654);    // offset 2, value 987654

Handling 64-bit Values

JavaScript numbers are IEEE-754 doubles and cannot safely represent the full 64-bit range. Use a high/low split or a third-party library such as long:

import Long from 'long';

const val = Long.fromString('123456789012345');
const buf = new ArrayBuffer(8);
const dv  = new DataView(buf);

dv.setInt32(0, val.high);  // high 32 bits
dv.setInt32(4, val.low);   // low 32 bits

Decoding Binary Back to Numbers

Retrieve the previous stored values:

const shortVal = dv.getInt16(0);
const intVal   = dv.getInt32(2);
const longVal  = Long.fromBits(dv.getInt32(4), dv.getInt32(0));

Complete round-trip example:

import Long from 'long';

const payload = new ArrayBuffer(14);
const v = new DataView(payload);

// write
v.setInt16(0, 42);
v.setInt32(2, 202404);
const l = Long.fromString('9223372036854775807');
v.setInt32(6, l.high);
v.setInt32(10, l.low);

// read
const a = v.getInt16(0);
const b = v.getInt32(2);
const c = Long.fromBits(v.getInt32(10), v.getInt32(6));