The concept of Meta-Classes is somewhat confusing, so we will go over a short example.
A meta-class is a class which is defined at run-time. A Contract is specified by an Application Binary Interface (ABI), which describes the methods and events it has. This description is passed the the object at run-time, and it creates a new Class, adding all the methods defined in the ABI at run-time.
Deploying a Contract
Most often, any contract you will need to interact with will already be deployed, but for this example will will first deploy the contract.
const bytecode = "0x608060405234801561001057600080fd5b506040516103bc3803806103bc83398101604081905261002f9161007c565b60405181815233906000907fddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef9060200160405180910390a333600090815260208190526040902055610094565b60006020828403121561008d578081fd5b5051919050565b610319806100a36000396000f3fe608060405234801561001057600080fd5b506004361061004c5760003560e01c8063313ce5671461005157806370a082311461006557806395d89b411461009c578063a9059cbb146100c5575b600080fd5b604051601281526020015b60405180910390f35b61008e610073366004610201565b6001600160a01b031660009081526020819052604090205490565b60405190815260200161005c565b604080518082018252600781526626bcaa37b5b2b760c91b6020820152905161005c919061024b565b6100d86100d3366004610222565b6100e8565b604051901515815260200161005c565b3360009081526020819052604081205482111561014b5760405162461bcd60e51b815260206004820152601a60248201527f696e73756666696369656e7420746f6b656e2062616c616e6365000000000000604482015260640160405180910390fd5b336000908152602081905260408120805484929061016a9084906102b6565b90915550506001600160a01b0383166000908152602081905260408120805484929061019790849061029e565b90915550506040518281526001600160a01b0384169033907fddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef9060200160405180910390a350600192915050565b80356001600160a01b03811681146101fc57600080fd5b919050565b600060208284031215610212578081fd5b61021b826101e5565b9392505050565b60008060408385031215610234578081fd5b61023d836101e5565b946020939093013593505050565b6000602080835283518082850152825b818110156102775785810183015185820160400152820161025b565b818111156102885783604083870101525b50601f01601f1916929092016040019392505050565b600082198211156102b1576102b16102cd565b500190565b6000828210156102c8576102c86102cd565b500390565b634e487b7160e01b600052601160045260246000fdfea2646970667358221220d80384ce584e101c5b92e4ee9b7871262285070dbcd2d71f99601f0f4fcecd2364736f6c63430008040033";
// A Human-Readable ABI; we only need to specify relevant fragments,
// in the case of deployment this means the constructor
const abi = [
"constructor(uint totalSupply)"
];
const factory = new hethers.ContractFactory(abi, bytecode, signer);
// Deploy, setting total supply to 100 tokens (assigned to the deployer)
const contract = await factory.deploy(100, {gasLimit: 300000});
// The contract is not currentl live on the network yet, however
// its address is ready for us
contract.address
// '0x0000000000000000000000000000000001c50c95'
// Wait until the contract has been deployed before interacting
// with it; returns the receipt for the deployemnt transaction
await contract.deployTransaction.wait();
// {
// to: null,
// from: '0x0000000000000000000000000000000001c31552',
// timestamp: '1645019704.914711762',
// contractAddress: '0x0000000000000000000000000000000001c50c95',
// gasUsed: 240000,
// logsBloom: null,
// transactionId: '0.0.29562194-1645019693-973691488',
// transactionHash: '0xfa56c87dced6e18cdd1638d44a2dc121eca38fbac8d0bc35310ff741f1378078707077069447d7bee06dec1876be3e12',
// logs: [
// {
// timestamp: '1645019704.914711762',
// address: '0x0000000000000000000000000000000001c50c95',
// data: '0x0000000000000000000000000000000000000000000000000000000000000064',
// topics: [Array],
// transactionHash: '0xfa56c87dced6e18cdd1638d44a2dc121eca38fbac8d0bc35310ff741f1378078707077069447d7bee06dec1876be3e12',
// logIndex: 0,
// transactionIndex: 0
// },
// ],
// cumulativeGasUsed: 240000,
// type: 0,
// byzantium: true,
// status: 1,
// accountAddress: null,
// events: [
// {
// timestamp: '1645019704.914711762',
// address: '0x0000000000000000000000000000000001c50c95',
// data: '0x0000000000000000000000000000000000000000000000000000000000000064',
// topics: [Array],
// transactionHash: '0xfa56c87dced6e18cdd1638d44a2dc121eca38fbac8d0bc35310ff741f1378078707077069447d7bee06dec1876be3e12',
// logIndex: 0,
// transactionIndex: 0,
// removeListener: [Function (anonymous)],
// getTransaction: [Function (anonymous)],
// getTransactionReceipt: [Function (anonymous)]
// },
// ]
// }
Connecting to a Contract
new hethers.Contract( address , abi , providerOrSigner )
Creating a new instance of a Contract connects to an existing contract by specifying its address, and its abi (used to populate the class' methods) a providerOrSigner.
// A Human-Readable ABI; for interacting with the contract, we
// must include any fragment we wish to use
const abi = [
// Read-Only Functions
"function balanceOf(address owner) view returns (uint256)",
"function decimals() view returns (uint8)",
"function symbol() view returns (string)",
// Authenticated Functions
"function transfer(address to, uint amount) returns (bool)",
// Events
"event Transfer(address indexed from, address indexed to, uint amount)"
];
const address = "0x0000000000000000000000000000000001c50c95";
// Read-Only; By connecting to a Provider, allows:
// - Populating Unsigned Transactions for non-constant methods
// - Querying Filters
const erc20 = new hethers.Contract(address, abi, provider);
// Read-Write; By connecting to a Signer, allows:
// - Everything from Read-Only
// - Any constant function
// - Static Calling non-constant methods
// - Sending transactions for non-constant/static functions
const erc20_rw = new hethers.Contract(address, abi, signer);
This is the address, the contract was constructed with.
If the Contract object is the result of a ContractFactory deployment, this is the transaction which was used to deploy the contract.
If a signer was provided to the constructor, this is that signer.
Returns a new instance of the Contract attached to a new address. This is useful if there are multiple similar or identical copies of a Contract on the network and you wish to interact with each of them.
Returns a new instance of the Contract, but connected to providerOrSigner.
Transfers amount tokens to target from the current signer. The return value (a boolean) is inaccessible during a write operation using a transaction. Other techniques (such as events) are required if this value is required. On-chain contracts calling the transfer function have access to this result, which is why it is possible.
If a provider was provided to the constructor, this is that provider. If a signer was provided that had a , this is that provider.
erc20.signer ⇒
Methods(inherited from )
erc20.attach( addressOrName ) ⇒
erc20.connect( providerOrSigner ) ⇒
By passing in a , this will return a downgraded Contract which only has read-only access (i.e. querying filters).
By passing in a . this will return a Contract which will act on behalf of that signer.
erc20.deployed( ) ⇒ Promise< >
Events(inheritted from )
Returns the number of decimal places used by this ERC-20 token. This can be used with when taking input from the user or when displaying the token amounts in the UI.
