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Run Bytes examples in the interactive playground
Type-Safe Primitive - Bytes16 provides compile-time guarantees for 16-byte values like UUIDs and medium hashes.

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Overview

Bytes16 is a branded Uint8Array type representing exactly 16 bytes (128 bits). It provides strict size validation and type safety for fixed-size byte values. 
import * as Bytes16 from 'tevm/primitives/Bytes/Bytes16';

// Create from hex
const bytes = Bytes16('0x' + '12'.repeat(16));
console.log(bytes.length); // 16

// Create zero-filled
const zeros = Bytes16.zero();
console.log(Bytes16.isZero(zeros)); // true

// Size is strictly enforced
Bytes16(new Uint8Array(15)); // Error: must be 16 bytes

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Use Cases

UUIDs (128-bit) 
const uuid = Bytes16('550e8400e29b41d4a716446655440000');
Medium Hashes 
// MD5, RIPEMD-128, etc.
const hash = Bytes16('0x...');
Fixed-Size Keys 
const key = Bytes16('0x' + 'ab'.repeat(16));

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Type Safety

Bytes16 uses Symbol branding for compile-time safety: 
type Bytes16Type = Uint8Array & {
  readonly [Symbol.for("Bytes16")]: true;
  readonly length: 16;
};
This prevents mixing different byte types: 
const bytes16 = Bytes16('0x' + '12'.repeat(16));
const bytes32 = Bytes32('0x' + '12'.repeat(32));

// Type error: cannot assign Bytes32 to Bytes16
const wrong: Bytes16.Bytes16Type = bytes32;

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Hex Variants

Bytes16 also supports hex string variants with case flags: 
// Lowercase hex (default)
type HexBytes16 = string & {
  readonly [Symbol.for("HexBytes16")]: true;
  readonly length: 34; // "0x" + 32 hex chars
  readonly lowercase: true;
};

// Uppercase hex
type HexBytes16Upper = string & {
  readonly [Symbol.for("HexBytes16")]: true;
  readonly length: 34;
  readonly uppercase: true;
};
For generic byte concepts, see Bytes.

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Constructors

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from

Create Bytes16 from hex string or bytes: 
// From hex
const b1 = Bytes16('0x' + '12'.repeat(16));

// From bytes
const b2 = Bytes16(Bytes16());

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fromHex

Create from hex string with strict validation: 
const bytes = Bytes16('0x1234567890abcdef1234567890abcdef');

// Without 0x prefix
const bytes2 = Bytes16('ab'.repeat(16));

// Throws on wrong length
Bytes16('0x1234'); // Error: must be 32 hex chars

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fromBytes

Create from Uint8Array with size check: 
const arr = Bytes16();
const bytes = Bytes16(arr);

// Throws on wrong size
Bytes16(new Uint8Array(15)); // Error

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zero

Create zero-filled Bytes16: 
const zeros = Bytes16.zero();
console.log(Bytes16.isZero(zeros)); // true

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Conversions

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toHex

Convert to hex string: 
const bytes = Bytes16(Bytes16());
const hex = Bytes16.toHex(bytes);
console.log(hex); // "0x00000000000000000000000000000000"

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toUint8Array

Convert to raw bytes: 
const bytes = Bytes16('0x' + '12'.repeat(16));
const arr = Bytes16.toUint8Array(bytes);
console.log(arr instanceof Uint8Array); // true

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Operations

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equals

Check equality: 
const a = Bytes16('0x' + 'aa'.repeat(16));
const b = Bytes16('0x' + 'aa'.repeat(16));
console.log(Bytes16.equals(a, b)); // true

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compare

Compare two values: 
const a = Bytes16('0x' + '01'.repeat(16));
const b = Bytes16('0x' + '02'.repeat(16));
console.log(Bytes16.compare(a, b)); // -1 (a < b)

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clone

Create independent copy: 
const original = Bytes16('0x' + '12'.repeat(16));
const copy = Bytes16.clone(original);

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isZero

Check if all zeros: 
const zeros = Bytes16.zero();
console.log(Bytes16.isZero(zeros)); // true

const nonZero = Bytes16('0x' + '00'.repeat(15) + '01');
console.log(Bytes16.isZero(nonZero)); // false

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size

Get size (always 16): 
const bytes = Bytes16('0x' + '12'.repeat(16));
console.log(Bytes16.size(bytes)); // 16

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Constants

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SIZE

Bytes16 size in bytes: 
console.log(Bytes16.SIZE); // 16

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ZERO

Zero-filled constant: 
console.log(Bytes16.ZERO.length); // 16
console.log(Bytes16.isZero(Bytes16.ZERO)); // true

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Error Handling

Bytes16 validates size strictly: 
try {
  Bytes16(new Uint8Array(15));
} catch (error) {
  console.log(error.code); // "BYTES16_INVALID_LENGTH"
  console.log(error.message); // "Bytes16 must be 16 bytes, got 15"
}

try {
  Bytes16('0x1234');
} catch (error) {
  console.log(error.code); // "BYTES16_INVALID_HEX_LENGTH"
  console.log(error.message); // "Bytes16 hex must be 32 characters..."
}
  • Bytes32 - 256-bit fixed-size bytes (most common)
  • Bytes64 - 512-bit fixed-size bytes
  • Keccak256 - 256-bit cryptographic hashes
  • Hex - Variable-length hex strings