Connecting Angular Application to a Smart Contract using Web3 Library
Smart contracts are digitally self-executing contracts that run on the Ethereum blockchain. Once they've been created they cannot change. Once they are deployed to a blockchain, their code cannot be updated like any other application.
How a Smart Contract Works?
A smart contract works like a vending machine by dispensing the item to a buyer and transferring cryptoCurrency payments instantly to a seller.
Steps to Integrate the Angular App to a Smart Contract
1) First step is to install web3.js using npm.
npm install web3 (This is the main package of web3.js)
2) You need a wallet account in order to make transactions.
I am using MetaMask
How to connect metamask to Application
<button (click)= "openMetaMask()"> Connect Wallet</button>
openMetaMask(){
this.contractService.openMetamask().then(resp =>{
})
}
Create a service and import web3.js into your service file. I've created a service called contract.service.ts.
import { Injectable } from '@angular/core';
import Web3 from "web3";
declare const window: any;
@Injectable({
providedIn: 'root'
})
export class ContractService {
window:any;
constructor() { }
private getAccounts = async () => {
try {
return await window.ethereum.request({ method: 'eth_accounts' });
} catch (e) {
return [];
}
}
public openMetamask = async () => {
window.web3 = new Web3(window.ethereum);
let addresses = await this.getAccounts();
console.log("service",addresses)
if (!addresses.length) {
try {
addresses = await window.ethereum.enable();
} catch (e) {
return false;
}
}
return addresses.length ? addresses[0] : null;
};
}
What is ABI and why it needs to interact with contracts?
The Application Binary Interface (ABI) is the way to interact with contracts in the Ethereum ecosystem both from outside the blockchain and from contract-to-contract interactions,
ABI is the interface between two program modules, one is often at the level of machine code. The interface is the de facto method for encoding/decoding data into/out of the machine code.
We need two things to interact
ABI
Address
and we can use Address and ABI in the same services
import { Injectable } from '@angular/core';
import Web3 from "web3";
declare const window: any;
const Address ='there will be address'
const abi = [
{
"inputs": [],
"stateMutability": "nonpayable",
"type": "constructor"
},
{
"anonymous": false,
"inputs": [
{
"indexed": false,
"internalType": "",
}
],
"name": "Token",
"type": "event"
},
]
ABI would be like that there is name Token which is actually the function name
@Injectable({
providedIn: 'root'
})
export class ContractService {
window:any;
constructor() { }
public Token = async () => {
try {
const contract = new window.web3.eth.Contract(
abi,
Address,
);
const token = await contract.methods.Token().call();
console.log("token",token)
return token
}
catch (error) {
const errorMessage = error.message;
console.log(errorMessage)
}
}
}
We are using the .call method instead of the .send method
.call for getting something and .send to send something.