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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.

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Signature

function toHex(calldata: CallDataType): string

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Parameters

  • calldata - CallData instance to convert

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Returns

string - Hex-encoded string with 0x prefix

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Examples

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

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

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

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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)

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Use Cases

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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();
}

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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");
}

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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}`;
}

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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;
  }
}

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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
}

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Comparison with 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

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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