Quick Start: JavaScript

Get started with @cofhe/sdk in a browser or Node.js app

Connect to an FHE-enabled contract, encrypt a value, send it on-chain, and decrypt the result — all from JavaScript.

Prerequisites

• Node.js 18+
• A deployed FHE contract on a supported network (e.g. Sepolia)
• A wallet with testnet ETH

1. Install

npm

npm install @cofhe/sdk@^0.5.1 viem

pnpm add @cofhe/sdk@^0.5.1 viem

yarn add @cofhe/sdk@^0.5.1 viem

2. Create and connect the client

Import from @cofhe/sdk/web for browser apps or @cofhe/sdk/node for Node.js scripts.

Web (browser)

import { createCofheConfig, createCofheClient } from '@cofhe/sdk/web';
import { chains } from '@cofhe/sdk/chains';
import { createPublicClient, createWalletClient, http, custom } from 'viem';
import { sepolia } from 'viem/chains';

// 1. Configure
const config = createCofheConfig({
  supportedChains: [chains.sepolia],
});
const client = createCofheClient(config);

// 2. Create viem clients (browser wallet)
const publicClient = createPublicClient({
  chain: sepolia,
  transport: http(),
});
const walletClient = createWalletClient({
  chain: sepolia,
  transport: custom(window.ethereum),
});

// 3. Connect
await client.connect(publicClient, walletClient);

import { createCofheConfig, createCofheClient } from '@cofhe/sdk/node';
import { chains } from '@cofhe/sdk/chains';
import { createPublicClient, createWalletClient, http } from 'viem';
import { sepolia } from 'viem/chains';
import { privateKeyToAccount } from 'viem/accounts';

// 1. Configure
const config = createCofheConfig({
  supportedChains: [chains.sepolia],
});
const client = createCofheClient(config);

// 2. Create viem clients
const account = privateKeyToAccount('0xYOUR_PRIVATE_KEY');
const publicClient = createPublicClient({
  chain: sepolia,
  transport: http(),
});
const walletClient = createWalletClient({
  chain: sepolia,
  transport: http(),
  account,
});

// 3. Connect
await client.connect(publicClient, walletClient);

If you use Ethers.js instead of viem, see the Client Setup guide for adapter usage.

3. Encrypt and send

import { Encryptable } from '@cofhe/sdk';

// Encrypt a uint32 value
const [encrypted] = await client
  .encryptInputs([Encryptable.uint32(42n)])
  .execute();

// Pass it to your contract
await contract.setValue(encrypted);

4. Decrypt for display

import { FheTypes } from '@cofhe/sdk';

// Create a permit (one-time per account + chain)
await client.permits.getOrCreateSelfPermit();

// Read the encrypted handle from your contract
const ctHash = await contract.storedValue();

// Decrypt locally
const plaintext = await client
  .decryptForView(ctHash, FheTypes.Uint32)
  .execute();

console.log(plaintext); // 42n

Next steps

• Client Setup — adapters, connection management, and config options.
• Encrypting Inputs — supported types, builder API, and progress callbacks.
• Permits — create, share, and manage decryption authorization.
• Decrypt to View — reveal encrypted state in your UI.
• Decrypt to Transact — decrypt with a verifiable signature for on-chain use.