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Fedor Katurov
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192
content/Blockchain/Common typescript examples.md
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192
content/Blockchain/Common typescript examples.md
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- Simple #dapp example for tests: [https://metamask.github.io/test-dapp/](https://metamask.github.io/test-dapp/)
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- Interaction with smart contracts described in [Smart contracts](Smart%20contracts.md)
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## Connecting to node
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If #Metamask extension installed, `Web3.givenProvider` is available in global window. You can use [Infura](https://infura.io) or your node instead:
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```typescript
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import Web3 from 'web3';
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// URL of your node
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const PROVIDER_URL = 'https://...';
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export const web3 = new Web3(Web3.givenProvider || PROVIDER_URL);
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```
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## Getting wallet balance
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```typescript
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const getBalance = async (address: string) => {
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return await web3.eth.getBalance(address);
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}
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```
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## Getting wallet address
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```typescript
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// first we need to authorize
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const authorize = async () => {
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await web3.currentProvider.request({ method: 'eth_requestAccounts' });
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}
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// then we can get wallet address
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const getCurrentAddressUser = () => {
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return web3.currentProvider.selectedAddress;
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}
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```
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## Sending transaction
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Sending `value` tokens with `memo` as value:
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```typescript
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const transfer = async ({
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from,
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to,
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value,
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memo,
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privateKey,
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gasLimit = 44000
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}) => {
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const nonce = await web3.eth.getTransactionCount(from);
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const gasPrice = await web3.eth.getGasPrice();
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const rawTx = {
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from,
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to,
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value: web3.utils.toHex(Web3.utils.toWei(value, 'ether')),
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gasLimit: web3.utils.toHex(gasLimit),
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gasPrice: web3.utils.toHex(gasPrice),
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nonce: web3.utils.toHex(nonce),
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data: memo,
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};
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const privateKeyBuffer = EthUtil.toBuffer(privateKey);
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const tx = new Transaction(rawTx);
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tx.sign(privateKeyBuffer);
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const serializedTx = tx.serialize();
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return this.web3.eth.sendSignedTransaction(
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`0x${serializedTx.toString('hex')}`
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);
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}
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```
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## Estimating transaction FEE
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Useful to get fixed amount of tokens from user with pre-estimated fee.
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```typescript
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import { web3 } from '.';
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const estimateFee = async ({
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from,
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to,
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value,
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memo,
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}) => {
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const gasPrice = await web3.eth.getGasPrice();
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const gasLimit = await web3.eth.estimateGas({
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from,
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to,
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value: web3.utils.toHex(web3.utils.toWei(value, 'ether')),
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data: web3.utils.asciiToHex(memo),
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}).call();
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return web3.utils.fromWei(
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BigInt(gasPrice.toString())
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.multiply(BigInt(gasLimit.toString()))
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.toString()
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);
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}
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```
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## Subscribing to wallet address change
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```typescript
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import { web3 } from '.';
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web3.currentProvider.on('accountsChanged', callback);
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```
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## Watching network change
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```typescript
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ethereum.on('chainChanged', handler: (chainId: string) => void);
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```
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## Adding custom token to wallet
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```typescript
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window.ethereum
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.request({
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method: 'wallet_watchAsset',
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params: {
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type: 'ERC20',
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options: {
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address: '0xb60e8dd61c5d32be8058bb8eb970870f07233155',
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symbol: 'FOO',
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decimals: 18,
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image: 'https://foo.io/token-image.svg',
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},
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},
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})
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.then((success) => {
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if (success) {
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console.log('FOO successfully added to wallet!')
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} else {
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throw new Error('Something went wrong.')
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}
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})
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.catch(console.error)
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```
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## Changing network to custom
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Checking current chainId:
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```typescript
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const getChainID = async () => {
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return ethereum.request({ method: 'eth_chainId' })
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}
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```
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Asking wallet to change current network:
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```typescript
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try {
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await window.ethereum.request({
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method: 'wallet_switchEthereumChain',
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params: [{ chainId: '0x03' }], // ropsten chainID (3) in hex
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});
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} catch (switchError) {
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// This error code indicates that the chain has not been added to MetaMask.
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if (error.code === 4902) {
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try {
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await window.ethereum.request({
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method: 'wallet_addEthereumChain',
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params: [{
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chainId: '0x03', // ropsten chainID (3) in hex
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chainName: 'Ropsten Test Network',
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nativeCurrency: {
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name: 'ETH',
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symbol: 'ETH',
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decimals: 18
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},
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rpcUrls: ['https://ropsten.infura.io/v3/9aa3d95b3bc440fa88ea12eaa4456161'],
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blockExplorerUrls: ['https://ropsten.etherscan.io']
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}] ,
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});
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} catch (addError) {
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// handle "add" error
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}
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}
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// handle other "switch" errors
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}
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```
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248
content/Blockchain/Smart contracts.md
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248
content/Blockchain/Smart contracts.md
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For common functions see [Common typescript examples](Common%20typescript%20examples.md).
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## Getting smart contract instance
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Useful for calling smart contract methods:
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```typescript
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import { Contract } from 'web3-eth-contract';
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import { web3 } from '.';
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const getContract = (abi: object, address?: string): Contract => {
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const abiFromJson = JSON.parse(JSON.stringify(abi));
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return new web3.eth.Contract(abiFromJson, address);
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};
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export default getContract;
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```
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## Executing contract method
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Contract has **read** and **write** methods. To get a list of methods, you can paste contract address on [https://etherscan.io/ ETH](https://etherscan.io/token/0xdac17f958d2ee523a2206206994597c13d831ec7#readContract) or any other service.
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**Read** methods doesn't require spending **gas**. **Write** methods cost some amount of **gas**, hence they will be executed with confirmation from user.
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### Example for #Metamask without private key
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```typescript
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// see example below
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import { getContract } from '.';
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// ABI of contract
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const CONTRACT_ABI = { /* ... */ };
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// address for contract
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const CONTRACT_ADDRESS = '0xdea164f67df4dbfe675d5271c9d404e0260f33bb';
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export const executeContractMethod = async ({}) => {
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// getting contract
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const contract = getContract(CONTRACT_ABI, CONTRACT_ADDRESS);
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// Calling write method
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try {
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// authorizing with Metamask
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await web3.currentProvider.request({ method: 'eth_requestAccounts' });
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// getting wallet address
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const addressUser = web3.currentProvider.selectedAddress;
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// calling "store" store method for contract
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// payload should include `from` address, that matches
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// current user's wallet
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await contract.methods.store(0, 'Parameter').send({
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from: addressUser,
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});
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} catch (e) {
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throw new Error(e);
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}
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// calling read method
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try {
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// this method can return data
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const result = await contract.methods.retrieve().call();
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} catch (e) {
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throw new Error(e);
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}
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}
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```
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### Node.js and React Native example
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```typescript
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// see example below
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import { getContract } from '.';
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// ABI контракта
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const CONTRACT_ABI = { /* ... */ };
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// contract address
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const CONTRACT_ADDRESS = '0xdea164f67df4dbfe675d5271c9d404e0260f33bb';
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// getting contract
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const contract = getContract(CONTRACT_ABI, CONTRACT_ADDRESS);
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// account's private key
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const privateKey = '...';
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// write-methods requires private key
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const executeContractMethod = async (val: number) => {
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const transaction = contract.methods.store(val);
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const account = web3.eth.accounts.privateKeyToAccount(privateKey);
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const options = {
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to: CONTRACT_ADDRESS,
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data: transaction.encodeABI(),
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gas: await transaction.estimateGas({ from: account.address }),
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gasPrice: await web3.eth.getGasPrice(),
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};
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const signed = await web3.eth.accounts.signTransaction(
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options,
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privateKey,
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);
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await web3.eth.sendSignedTransaction(signed.rawTransaction!);
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};
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```
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### Calling a batch of contract's methods
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Function calls batch of requests, returning array of results. For example:
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```typescript
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const requests = [
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contract.method.balanceOf().call,
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contract.method.getStaked().call
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]
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const result = await makeBatchRequest(request);
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```
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```typescript
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const web3 = new Web3(Web3.givenProvider || PROVIDER_URL);
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const makeBatchRequest = (calls: any[]) => {
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try {
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const web3 = getWeb3NoAccount();
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const batch = new web3.BatchRequest();
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const promises = calls.map((call) => {
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return new Promise((resolve, reject) => {
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batch.add(
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call.request({}, (err, result) => {
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if (err) {
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reject(err);
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} else {
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resolve(result);
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}
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})
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);
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});
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});
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batch.execute();
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return Promise.all(promises);
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} catch {
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return null;
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}
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};
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export default makeBatchRequest;
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```
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## Subscribing to smart contract events
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There're different ways to subscribe for contract events. For all of them you will need following variables:
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```typescript
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import Web3 from 'web3';
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const web3 = new Web3('YOUR_RPC_ENDPOINT_HERE');
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const ABI = 'YOUR ABI HERE';
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const CONTRACT_ADDRESS = 'YOUR CONTRACT ADDRESS HERE';
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const myContract = new Web3.Contract(ABI, CONTRACT_ADDRESS);
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```
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### By accessing contract.events
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```typescript
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referralProgramContract.events
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.RegisterUser()
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.on('connected', (subscriptionId: string) => {
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console.log(`| UserRegistered | events | ${subscriptionId}`);
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})
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.on(
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'data',
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async (event: {
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removed: boolean;
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returnValues: RegisterUserResponseInterface;
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}) => {
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try {
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if (event.removed) {
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return;
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}
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const { user, referrer } = event.returnValues;
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console.log(user, referrer);
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} catch (e) {
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console.log(`| ONCE | ${e}`);
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}
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},
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)
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.on('error', (error: ErrnoException) => {
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console.log(error);
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});
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```
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### With filtering
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We're listening to `Transfer` event here:
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```typescript
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let options = {
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filter: {
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value: [],
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},
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fromBlock: 0
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};
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myContract.events.Transfer(options)
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.on('data', event => console.log(event))
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.on('changed', changed => console.log(changed))
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.on('error', err => throw err)
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.on('connected', str => console.log(str))
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```
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### Common Subscribe method
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Filtering options can also be specified:
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```typescript
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let options = {
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fromBlock: 0,
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address: ['address-1', 'address-2'], //Only get events from specific addresses
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topics: [] //What topics to subscribe to
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};
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let subscription = ('logs', options, (err,event) => {
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if (!err)
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console.log(event)
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});
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subscription.on('data', event => console.log(event))
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subscription.on('changed', changed => console.log(changed))
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subscription.on('error', err => { throw err })
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subscription.on('connected', nr => console.log(nr))
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```
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### Getting event history
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Getting history for `Transfer` events for specific values. More info can be found [here](https://web3js.readthedocs.io/en/v1.2.11/web3-eth-subscribe.html#)
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```typescript
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//example options(optional)
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let options = {
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filter: {
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// only get events where transfer value was 1000 or 1337
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value: ['1000', '1337']
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},
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// number | "earliest" | "pending" | "latest"
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fromBlock: 0,
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toBlock: 'latest'
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};
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myContract.getPastEvents('Transfer', options)
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.then(results => console.log(results))
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.catch(err => throw err);
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```
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