toHex

Converts CallData to a hex-encoded string with 0x prefix. Primary method for serializing calldata for display or transmission.

WASM performance note: Simple string/hex conversions like toHex() usually do not get faster under WASM. Crossing the JS↔WASM boundary adds overhead, and JavaScript already has very fast built-ins for hex/string formatting. Prefer the default JS entrypoint for toHex()-style operations; reserve WASM for compute-heavy tasks (e.g., Keccak256 hashing, ABI/RLP encoding/decoding, secp256k1/BLS) where it shines.Voltaire’s WASM builds intentionally balance performance and bundle size. For maximum performance, build from source using the performance-optimized WASM target. See Build from Source: /dev/build-system#typescript-targets and WASM Build Modes: /dev/wasm#build-modes.

Signature

Namespace
Class

function toHex(calldata: CallDataType): string

calldata.toHex(): string

Parameters

calldata - CallData instance to convert

Returns

string - Hex-encoded string with 0x prefix

Examples

Basic Usage
Transaction Serialization
Class API

import { CallData } from '@tevm/voltaire';

const calldata = CallData("0xa9059cbb...");
const hex = CallData.toHex(calldata);

console.log(hex);
// "0xa9059cbb000000000000000000000000..."

import { CallData, Transaction } from '@tevm/voltaire';

const calldata = abi.transfer.encode(recipient, amount);

const tx = Transaction({
  to: tokenAddress,
  data: calldata,
  // ... other fields
});

// Serialize transaction
const txData = {
  to: tx.to.toHex(),
  data: CallData.toHex(tx.data), // Hex for JSON-RPC
  value: tx.value.toString(),
};

import { CallData } from '@tevm/voltaire';

const calldata = CallData("0xa9059cbb...");
const hex = calldata.toHex(); // Method on instance

console.log(hex);

Format

Output always includes 0x prefix and lowercase hex:

import { CallData } from '@tevm/voltaire';

const calldata = CallData.fromBytes(
  new Uint8Array([0xa9, 0x05, 0x9c, 0xbb])
);

console.log(CallData.toHex(calldata));
// "0xa9059cbb" (lowercase, with prefix)

Use Cases

JSON-RPC Transactions

import { CallData } from '@tevm/voltaire';

async function sendTransaction(calldata: CallDataType) {
  const response = await fetch(rpcUrl, {
    method: 'POST',
    body: JSON.stringify({
      jsonrpc: '2.0',
      method: 'eth_sendTransaction',
      params: [{
        to: tokenAddress.toHex(),
        data: CallData.toHex(calldata), // Required hex format
      }],
    }),
  });

  return response.json();
}

Logging and Debugging

import { CallData } from '@tevm/voltaire';

function logCallData(calldata: CallDataType) {
  const hex = CallData.toHex(calldata);
  const selector = CallData.getSelector(calldata);

  console.log("CallData:", hex);
  console.log("Selector:", Hex.fromBytes(selector));
  console.log("Size:", calldata.length, "bytes");
}

Block Explorers

import { CallData } from '@tevm/voltaire';

function generateExplorerLink(
  tx: Transaction,
  chainId: number
): string {
  const calldata = CallData.toHex(tx.data);
  const baseUrl = getExplorerUrl(chainId);

  return `${baseUrl}/tx/${tx.hash}?data=${calldata}`;
}

Storage and Caching

import { CallData } from '@tevm/voltaire';

class CallDataCache {
  private cache = new Map<string, CallDataDecoded>();

  async get(calldata: CallDataType): Promise<CallDataDecoded> {
    const key = CallData.toHex(calldata);

    if (this.cache.has(key)) {
      return this.cache.get(key)!;
    }

    const decoded = CallData.decode(calldata, abi);
    this.cache.set(key, decoded);
    return decoded;
  }
}

Performance

String conversion is optimized but has overhead:

// Benchmark: 1M iterations
const calldata = CallData.fromBytes(
  new Uint8Array(68) // 4 + 32 + 32 bytes
);

console.time("toHex");
for (let i = 0; i < 1_000_000; i++) {
  CallData.toHex(calldata);
}
console.timeEnd("toHex");

// Pure JS: ~120ms
// Native: ~45ms (2.7x faster)

For performance-critical paths, keep data as Uint8Array:

// Faster: Work with bytes
function processCallData(calldata: CallDataType) {
  const selector = CallData.getSelector(calldata); // No conversion
  // Process bytes directly
}

// Slower: Convert to hex first
function processCallDataSlow(calldata: CallDataType) {
  const hex = CallData.toHex(calldata); // Conversion overhead
  const selector = hex.slice(0, 10); // String manipulation
}

Comparison with toBytes

toHex
toBytes

import { CallData } from '@tevm/voltaire';

const calldata = CallData.fromBytes(
  new Uint8Array([0xa9, 0x05, 0x9c, 0xbb])
);

const hex = CallData.toHex(calldata);
console.log(hex); // "0xa9059cbb"
console.log(typeof hex); // "string"

Use when:

Displaying to users
Sending over JSON-RPC
Storing as text
Logging/debugging

import { CallData } from '@tevm/voltaire';

const calldata = CallData("0xa9059cbb");
const bytes = CallData.toBytes(calldata);

console.log(bytes); // Uint8Array(4) [169, 5, 156, 187]
console.log(bytes instanceof Uint8Array); // true

Use when:

Binary protocols
Performance-critical
Direct byte manipulation
WASM interop

Type Safety

Output is plain string (no branding):

import { CallData, type CallDataType } from '@tevm/voltaire';

const calldata: CallDataType = CallData("0xa9059cbb");
const hex: string = CallData.toHex(calldata);

// Cannot convert back without constructor
const calldata2: CallDataType = hex; // ❌ Type error
const calldata3: CallDataType = CallData(hex); // ✅ Correct

toBytes - Convert to Uint8Array
fromHex - Parse hex string
Hex - Hex encoding utilities
decode - Decode to structured form

Overview

Getting Started

Core Concepts

Skills

JSONRPCProvider

Contract

Primitives

Cryptography

EVM

Utils

Guides

Examples

Swift

Zig

Developer Documentation

Generated API (TypeDoc)

Signature

Parameters

Returns

Examples

Format

Use Cases

JSON-RPC Transactions

Logging and Debugging

Block Explorers

Storage and Caching

Performance

Comparison with toBytes

Type Safety

​Signature

​Parameters

​Returns

​Examples

​Format

​Use Cases

​JSON-RPC Transactions

​Logging and Debugging

​Block Explorers

​Storage and Caching

​Performance

​Comparison with toBytes

​Type Safety

​Related

Signature

Parameters

Returns

Examples

Format

Use Cases

JSON-RPC Transactions

Logging and Debugging

Block Explorers

Storage and Caching

Performance

Comparison with toBytes

Type Safety

Related