ERC20 Approve

Search…
ERC20 Approve
If you have replaced your web3 provider with Fortmatic provider, nothing needs to be changed for web3 ERC20 transaction to continue working. The following is an example on how to initiate an ERC20 token Approve.
Note that this ERC20 custom view will be displayed only on the mainnet, otherwise Generic Contract Call view will be displayed.
Web3 Pre-1.0 Stable Versions
Web3 1.0 Beta Version
1
// Initialize provider
2
import Fortmatic from 'fortmatic';
3
import Web3 from 'web3';
4
​
5
const fm = new Fortmatic('YOUR_API_KEY');
6
window.web3 = new Web3(fm.getProvider());
7
​
8
// Get the contract ABI from compiled smart contract json
9
const erc20TokenContractAbi = [{"constant":true,"inputs":[],"name":"name","outputs":[{"name":"","type":"string"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"name":"spender","type":"address"},{"name":"tokens","type":"uint256"}],"name":"approve","outputs":[{"name":"success","type":"bool"}],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[],"name":"totalSupply","outputs":[{"name":"","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"name":"from","type":"address"},{"name":"to","type":"address"},{"name":"tokens","type":"uint256"}],"name":"transferFrom","outputs":[{"name":"success","type":"bool"}],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[],"name":"decimals","outputs":[{"name":"","type":"uint8"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"name":"amount","type":"uint256"}],"name":"withdrawEther","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[],"name":"_totalSupply","outputs":[{"name":"","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[{"name":"tokenOwner","type":"address"}],"name":"balanceOf","outputs":[{"name":"balance","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[],"name":"acceptOwnership","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[],"name":"owner","outputs":[{"name":"","type":"address"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"symbol","outputs":[{"name":"","type":"string"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[{"name":"a","type":"uint256"},{"name":"b","type":"uint256"}],"name":"safeSub","outputs":[{"name":"c","type":"uint256"}],"payable":false,"stateMutability":"pure","type":"function"},{"constant":false,"inputs":[{"name":"to","type":"address"},{"name":"tokens","type":"uint256"}],"name":"transfer","outputs":[{"name":"success","type":"bool"}],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[{"name":"a","type":"uint256"},{"name":"b","type":"uint256"}],"name":"safeDiv","outputs":[{"name":"c","type":"uint256"}],"payable":false,"stateMutability":"pure","type":"function"},{"constant":false,"inputs":[{"name":"spender","type":"address"},{"name":"tokens","type":"uint256"},{"name":"data","type":"bytes"}],"name":"approveAndCall","outputs":[{"name":"success","type":"bool"}],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[{"name":"a","type":"uint256"},{"name":"b","type":"uint256"}],"name":"safeMul","outputs":[{"name":"c","type":"uint256"}],"payable":false,"stateMutability":"pure","type":"function"},{"constant":true,"inputs":[],"name":"newOwner","outputs":[{"name":"","type":"address"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"name":"tokenAddress","type":"address"},{"name":"tokens","type":"uint256"}],"name":"transferAnyERC20Token","outputs":[{"name":"success","type":"bool"}],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[{"name":"tokenOwner","type":"address"},{"name":"spender","type":"address"}],"name":"allowance","outputs":[{"name":"remaining","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[{"name":"a","type":"uint256"},{"name":"b","type":"uint256"}],"name":"safeAdd","outputs":[{"name":"c","type":"uint256"}],"payable":false,"stateMutability":"pure","type":"function"},{"constant":false,"inputs":[{"name":"_newOwner","type":"address"}],"name":"transferOwnership","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"inputs":[],"payable":false,"stateMutability":"nonpayable","type":"constructor"},{"payable":true,"stateMutability":"payable","type":"fallback"},{"anonymous":false,"inputs":[{"indexed":true,"name":"_from","type":"address"},{"indexed":true,"name":"_to","type":"address"}],"name":"OwnershipTransferred","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"name":"from","type":"address"},{"indexed":true,"name":"to","type":"address"},{"indexed":false,"name":"tokens","type":"uint256"}],"name":"Transfer","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"name":"tokenOwner","type":"address"},{"indexed":true,"name":"spender","type":"address"},{"indexed":false,"name":"tokens","type":"uint256"}],"name":"Approval","type":"event"}];
10
​
11
// Create contract object
12
const tokenContract = web3.eth.contract(erc20TokenContractAbi);
13
​
14
// Instantiate contract
15
const tokenContractInstance = tokenContract.at('0x8EBC7785b83506AaA295Bd9174e6A7Ad5681fb80');
16
const toAddress = '0xE0cef4417a772512E6C95cEf366403839b0D6D6D';
17
​
18
// Calculate contract compatible value for approve with proper decimal points using BigNumber
19
const tokenDecimals = web3.toBigNumber(18);
20
const tokenAmountToApprove = web3.toBigNumber(999000000000);
21
const calculatedApproveValue = web3.toHex(tokenAmountToApprove.mul(web3.toBigNumber(10).pow(tokenDecimals)));
22
​
23
// Get user account wallet address first
24
web3.eth.getAccounts(function(error, accounts) {
25
  if (error) throw error;
26
  // Send ERC20 transaction with web3
27
  tokenContractInstance.approve.sendTransaction(toAddress, calculatedApproveValue, {from: accounts[0]}, function(error, txnHash) {
28
    if (error) throw error;
29
    console.log(txnHash);
30
  });
31
});
Copied!
1
// Initialize provider
2
import Fortmatic from 'fortmatic';
3
import Web3 from 'web3';
4
​
5
const fm = new Fortmatic('YOUR_API_KEY');
6
window.web3 = new Web3(fm.getProvider());
7
​
8
// Get the contract ABI from compiled smart contract json
9
const erc20TokenContractAbi = [{"constant":true,"inputs":[],"name":"name","outputs":[{"name":"","type":"string"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"name":"spender","type":"address"},{"name":"tokens","type":"uint256"}],"name":"approve","outputs":[{"name":"success","type":"bool"}],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[],"name":"totalSupply","outputs":[{"name":"","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"name":"from","type":"address"},{"name":"to","type":"address"},{"name":"tokens","type":"uint256"}],"name":"transferFrom","outputs":[{"name":"success","type":"bool"}],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[],"name":"decimals","outputs":[{"name":"","type":"uint8"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"name":"amount","type":"uint256"}],"name":"withdrawEther","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[],"name":"_totalSupply","outputs":[{"name":"","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[{"name":"tokenOwner","type":"address"}],"name":"balanceOf","outputs":[{"name":"balance","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[],"name":"acceptOwnership","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[],"name":"owner","outputs":[{"name":"","type":"address"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"symbol","outputs":[{"name":"","type":"string"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[{"name":"a","type":"uint256"},{"name":"b","type":"uint256"}],"name":"safeSub","outputs":[{"name":"c","type":"uint256"}],"payable":false,"stateMutability":"pure","type":"function"},{"constant":false,"inputs":[{"name":"to","type":"address"},{"name":"tokens","type":"uint256"}],"name":"transfer","outputs":[{"name":"success","type":"bool"}],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[{"name":"a","type":"uint256"},{"name":"b","type":"uint256"}],"name":"safeDiv","outputs":[{"name":"c","type":"uint256"}],"payable":false,"stateMutability":"pure","type":"function"},{"constant":false,"inputs":[{"name":"spender","type":"address"},{"name":"tokens","type":"uint256"},{"name":"data","type":"bytes"}],"name":"approveAndCall","outputs":[{"name":"success","type":"bool"}],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[{"name":"a","type":"uint256"},{"name":"b","type":"uint256"}],"name":"safeMul","outputs":[{"name":"c","type":"uint256"}],"payable":false,"stateMutability":"pure","type":"function"},{"constant":true,"inputs":[],"name":"newOwner","outputs":[{"name":"","type":"address"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"name":"tokenAddress","type":"address"},{"name":"tokens","type":"uint256"}],"name":"transferAnyERC20Token","outputs":[{"name":"success","type":"bool"}],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[{"name":"tokenOwner","type":"address"},{"name":"spender","type":"address"}],"name":"allowance","outputs":[{"name":"remaining","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[{"name":"a","type":"uint256"},{"name":"b","type":"uint256"}],"name":"safeAdd","outputs":[{"name":"c","type":"uint256"}],"payable":false,"stateMutability":"pure","type":"function"},{"constant":false,"inputs":[{"name":"_newOwner","type":"address"}],"name":"transferOwnership","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"inputs":[],"payable":false,"stateMutability":"nonpayable","type":"constructor"},{"payable":true,"stateMutability":"payable","type":"fallback"},{"anonymous":false,"inputs":[{"indexed":true,"name":"_from","type":"address"},{"indexed":true,"name":"_to","type":"address"}],"name":"OwnershipTransferred","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"name":"from","type":"address"},{"indexed":true,"name":"to","type":"address"},{"indexed":false,"name":"tokens","type":"uint256"}],"name":"Transfer","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"name":"tokenOwner","type":"address"},{"indexed":true,"name":"spender","type":"address"},{"indexed":false,"name":"tokens","type":"uint256"}],"name":"Approval","type":"event"}];
10
​
11
// Create contract object
12
const tokenContractAddress = '0x8EBC7785b83506AaA295Bd9174e6A7Ad5681fb80';
13
​
14
// Instantiate contract
15
const tokenContract = new web3.eth.Contract(erc20TokenContractAbi, tokenContractAddress);
16
const toAddress = '0xE0cef4417a772512E6C95cEf366403839b0D6D6D';
17
​
18
// Calculate contract compatible value for approve with proper decimal points using BigNumber
19
const tokenDecimals = web3.utils.toBN(18);
20
const tokenAmountToApprove = web3.utils.toBN(999000000000);
21
const calculatedApproveValue = web3.utils.toHex(tokenAmountToApprove.mul(web3.utils.toBN(10).pow(tokenDecimals)));
22
​
23
// Get user account wallet address first
24
web3.eth.getAccounts().then((accounts) => {
25
  // Send ERC20 transaction with web3
26
  tokenContract.methods.approve(
27
    toAddress, 
28
    calculatedApproveValue
29
  ).send({from: accounts[0]})
30
  .once('transactionHash', (hash) => { console.log(hash); })
31
  .once('receipt', (receipt) => { console.log(receipt); });
32
});
Copied!
Smart Contract - Previous
ERC20 Transfer
Next - Smart Contract
ERC20 TransferFrom
Last modified 1yr ago
Copy link