Alchemy Web3

Web3 client extended with Alchemy and browser provider integration.

Introduction

Alchemy Web3 provides website authors with a drop-in replacement for the web3.js Ethereum API client. It produces a client matching that of web3.js, but brings two advantages to make use of Alchemy API:

• Uses Alchemy or an injected provider as needed. Most requests will be sent through Alchemy, but requests involving signing and sending transactions are sent via a browser provider like Metamask or Trust Wallet if the user has it installed, or via a custom provider specified in options.

• Easy access to Alchemy's higher-order APIs. The client exposes methods to call Alchemy's exclusive features.

Alchemy Web3 is designed to require minimal configuration so you can start using it in your app right away.

Installation

With Yarn:

yarn add @alch/alchemy-web3

Or with NPM:

npm install @alch/alchemy-web3

You will also need an Alchemy account to access the Alchemy API. If you don't have one yet, contact Alchemy to request one.

Usage

Basic Usage

Create the client by importing the function createAlchemyWeb3 and then passing it your Alchemy app's URL:

import { createAlchemyWeb3 } from "@alch/alchemy-web3";

const ALCHEMY_URL = "https://eth-mainnet.alchemyapi.io/jsonrpc/<api-key>";

const web3 = createAlchemyWeb3(ALCHEMY_URL);

You can use any of the methods described in the web3.js API and they will send requests to Alchemy:

// Many web3.js methods return promises.
web3.eth.getBlock("latest").then(block => {
  /* … */
});

web3.eth
  .estimateGas({
    from: "0xge61df…",
    to: "0x087a5c…",
    data: "0xa9059c…",
    gasPrice: "0xa994f8…",
  })
  .then(gasAmount => {
    /* … */
  });

With a Browser Provider

If the user has a provider in their browser available at window.ethereum, then any methods which involve user accounts or signing will automatically use it. This provider might be injected by Metamask, Trust Wallet, or other browsers or browser extensions if the user has them installed. For example, the following will use a provider from the user's browser:

web3.eth.getAccounts().then(accounts => {
  web3.eth.sendTransaction({
    from: accounts[0],
    to: "0x6A823E…",
    value: "1000000000000000000",
  });
});

Note on using Metamask

As just discussed, Metamask will automatically be used for accounts and signing if it is installed. However, for this to work you must first request permission from the user to access their accounts in Metamask. This is a security restriction required by Metamask: details can be found here.

To enable the use of Metamask, you must call ethereum.enable(). An example of doing so is as follows:

if (window.ethereum) {
  ethereum
    .enable()
    .then(accounts => {
      // Metamask is ready to go!
    })
    .catch(reason => {
      // Handle error. Likely the user rejected the login.
    });
} else {
  // The user doesn't have Metamask installed.
}

Note that doing so will display a Metamask dialog to the user if they have not already seen it and accepted, so you may choose to wait to enable Metamask until the user is about to perform an action which requires it. This is also why Alchemy Web3 will not automatically enable Metamask on page load.

With a custom provider

You may also choose to bring your own provider for writes rather than relying on one being present in the browser environment. To do so, pass your provider options object when creating your Alchemy Web3 instance using the writeProvider key:

const web3 = createAlchemyWeb3(ALCHEMY_URL: { writeProvider: provider });

Your provider should expose at least one of sendAsync() or send(), as specified in EIP 1193.

You may swap out the custom provider at any time by calling the setWriteProvider() method:

web3.setWriteProvider(provider);

Alchemy Higher-Order APIs

The produced client also grants easy access to Alchemy's higher-order APIs. Currently, this is the following method.

web3.alchemy.tokenBalances(address, contractAddresses)

Returns token balances for a specific address given a list of contracts.

Parameters:

• address: The address for which token balances will be checked.
• contractAddresses: An array of contract addresses.

Returns:

An object with the following fields:

• address: The address for which token balances were checked.
• tokenBalances: An array of token balance objects. Each object contains:
  • contractAddress: The address of the contract.
  • tokenBalance: The balance of the contract, as a string representing a base-10 number.
  • error: An error string. One of this or tokenBalance will be null.

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