As we continue to evolve and improve the Hedera ecosystem, we are committed to ensuring that our developer tools and resources remain easy to use and up-to-date. With this goal in mind, the Hethers.js library will be deprecated by October 20, 2023.
🚨 The documentation site will be taken offline on January 31, 2024.
Installing
Hethers' various Classes and Functions are available to import manually from sub-packages under the organization but for most projects, the umbrella package is the easiest way to get started.
npm install --save @hashgraph/hethers
Importing
NodeJS
// node.js require
const { hethers } = require('@hashgraph/hethers');
// ES6 or TypeScript
import { hethers } from '@hashgraph/hethers';
Web Browser
// ES6 in the Browser
<script type="module">
import { hethers } from "hethers.esm.min.js";
// Your code here...
</script>
// ES3(UMD) in the Browser
<script src="<link>hethers.umd.min.js" type="application/javascript"></script>
Common terminology
Name
Purpose
Provider
A Provider (in hethers) is a class which provides an abstraction for a connection to the Hedera Network.
Signer
A Signer is a class that (usually) in some way directly or indirectly has access to a private key, which can sign messages and transactions to authorize the network to charge your account hbar to perform operations.
Contract
A Contract is an abstraction that represents a connection to a specific contract on the Hedera Network, so that applications can use it as a normal JavaScript object.
Connecting to Hedera Providers
// available default providers ['mainnet', 'testnet', 'previewnet']
const defaultProvider = hethers.providers.getDefaultProvider('testnet');
// or you can define the connection properties by yourself
const customProvider = new hethers.providers.HederaProvider(
nodeId, // AccountLike
consensusNodeUrl, // string
mirrorNodeUrl // string
);
const tx = signer.sendTransaction({
to: '0.0.29562194',
value: hethers.utils.parseHbar("1.2")
});
Contracts
A Contract is an abstraction of program code that lives on the Hedera Hashgraph Smart Contract Service.
If you are familiar with Databases, this is similar to an Object Relational Mapper (ORM).
In order to communicate with the Contract on-chain, this class needs to know what methods are available and how to encode and decode the data, which is what the Application Binary Interface (ABI) provides.
This class is a meta-class, which means its methods are constructed at runtime, and when you pass in the ABI to the constructor it uses it to determine which methods to add.
While an on-chain Contract may have many methods available, you can safely ignore any methods you don't need or use, providing a smaller subset of the ABI to the contract.
An ABI often comes from the Solidity compiler, but you can use the Human-Readable ABI in code, which the following examples use.
const provider = hethers.providers.getDefaultProvider('testnet');
// The contract address
const erc20Address = '0x0000000000000000000000000000000001d5a8f0';
// The ERC-20 Contract ABI, which is a common contract interface
// for tokens (this is the Human-Readable ABI format)
const erc20Abi = [
// Some details about the token
'function name() view returns (string)',
'function symbol() view returns (string)',
// Get the account balance
'function balanceOf(address) view returns (uint)',
// Send some of your tokens to someone else
'function transfer(address to, uint amount)',
// An event triggered whenever anyone transfers to someone else
'event Transfer(address indexed from, address indexed to, uint amount)'
];
// The Contract object
const contract = new hethers.Contract(erc20Address, erc20Abi, provider);
Read-Only Methods
// The Contract is currently connected to the Provider.
// You need to connect to a Signer, so
// that you can pay for ContractLocalCall transactions.
const contractWithSigner = contract.connect(signer);
// Get the ERC-20 token name
await contractWithSigner.name({gasLimit: 30000});
// 'My Token Name'
// Get the ERC-20 token symbol (for tickers and UIs)
await contractWithSigner.symbol({gasLimit: 30000});
// 'MTN'
// Get the balance of an address
await contractWithSigner.balanceOf(contractWallet.address, {gasLimit: 30000});
// BigNumber { _hex: '0x2710', _isBigNumber: true }
State Changing Methods
const amount = hethers.utils.parseUnits('1.0');
// Send 10**8 amount of tokens to the recipient's address
const tx = contractWithSigner.transfer(
'0x0000000000000000000000000000000001d5a949',
amount,
{gasLimit: 50000}
);
Listening to Events
// Receive an event when ANY transfer occurs
contract.on('Transfer', (from, to, amount, event) => {
console.log(`${from} sent ${formatHbar(amount)} to ${to}`);
});
// A filter for when a specific address receives tokens
const filter = contract.filters.Transfer(null, signer.address);
// {
// address: '0x0000000000000000000000000000000001c4fff6',
// topics: [
// '0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef',
// null,
// '0x0000000000000000000000000000000000000000000000000000000001c42506'
// ]
// }
// Receive an event when that filter occurs
contract.on(filter, (from, to, amount, event) => {
// The to will always be "address"
console.log(`I got ${formatHbar(amount)} from ${from}.`);
});
// To sign a simple string, which are used for
// logging into a service, pass the string in.
signer.signMessage('message');
// '0xe1c58c8ea54a270eb99c14e1e6f7bbb14f2a16225556e5e7cc27e77d0f57cad4611fd46c747430e6b9df9cd51fa8430c993f664789034525629742f3ebb0be6d1c'
// A common case is also signing a hash, which is 32
// bytes. It is important to note, that to sign binary
// data it MUST be an Array (or TypedArray)
// This string is 66 characters long
const message = '0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef';
// This array representation is 32 bytes long
const messageBytes = hethers.utils.arrayify(message);
// To sign a hash, you most often want to sign the bytes
const signature = await signer.signMessage(messageBytes);
// '0x6a8241ec5885dd54f59dd0a4219490bba63e19473de9ba6895c5bfa5fb4fe0c03e761e79f1a5655b2b8e7119adbd1ec09df829884a4d514d45ec89b66eb951791b'
Once you have a , you have a read-only connection to the blockchain, which you can use to query the current state, fetch historic logs, look up deployed code and so on.
The object makes it easier to use an on-chain Contract as a normal JavaScript object, with the methods mapped to encoding and decoding data for you.
