Wallet Setup

Set up a wallet for contract deployment and execution

Key Management with MetaMask

Developers can manage Ethereum wallet private keys using the MetaMask browser add-on.

MetaMask is a non-custodial wallet. The user's private key is encoded with the mnemonic phrase and stored in user's local browser. Once lost, the user can no longer control the savings or restore access to the wallet. MetaMask communicates with Ethereum Ledger via Infura. Please refer to the MetaMask website for more details.

Initialize Web3

First, install the following in your dApp:

npm install --save web3

Create a new file, name it web3.js and insert the following code in it:

import Web3 from 'web3';

const getWeb3 = () => new Promise((resolve) => {
 window.addEventListener('load', () => {
     let currentWeb3;

     if (window.ethereum) {
         currentWeb3 = new Web3(window.ethereum);
         try {
             // Request account access if needed
             window.ethereum.enable();
             // Accounts now exposed
             resolve(currentWeb3);
         } catch (error) {
             // User denied account access...
             alert('Please allow access for the app to work');
         }
     } else if (window.web3) {
         window.web3 = new Web3(web3.currentProvider);
         // Accounts always exposed
         resolve(currentWeb3);
     } else {
         console.log('Non-Ethereum browser detected. You should consider trying MetaMask!');
     }
 });
});

export default getWeb3;

To put it simply, you can inject the global object ethereum if you have added MetaMask to Chrome.

Next, import the code as below:

import getWeb3 from '/path/to/web3';

Call the function:

  getWeb3()
 .then((result) => {
     this.web3 = result;// we instantiate our contract next
 });

Set up Account

We need an account from the web3 instance we created above to send transactions.

  this.web3.eth.getAccounts()
 .then((accounts) => {
     this.account = accounts[0];
 })

The getAccounts() function returns all the user’s Metamask accounts, whileaccounts[0] is the one currently selected by the user.

Initialize Contract

Initialize your contract after completing above steps.

Call Functions

Now you can call any function by directly interacting with the instantiated contract. Please note that:

Functions that do not alter the state of the contract are call() functions. Below is an example of calling a call() function:

  this.myContractInstance.methods.myMethod(myParams)
    .call()
    .then(
        // do stuff with returned values
    )

Functions that alter the state of the contract are send() functions. Below is an example of calling a send() function:

this.myContractInstance.methods.myMethod(myParams)
.send({
from: this.account,gasPrice: 0
}).then (
(receipt) => {
  // returns a transaction receipt}
);

Move Assets from Ethereum to Ontology

Ontology supports developers to conduct cross-chain asset transfer using PolyBridge.