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Drop-in web3 solution for single-page Ethereum dApps
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This package is now deprecated. Please refer to web3-react.

Web3: Webpacked

Building your dApp in React? Check out the sibling React library, web3-webpacked-react!

Example GIF

This project is a drop-in solution for single-page Ethereum dApps. It's a webpacked library consisting of:

  • A robust management framework for the global web3 object injected into browsers by MetaMask, Trust, etc. The framework exposes an instantiated web3.js instance, keeps variables such as the current network and default account up-to-date, and fires customizable handlers when key events occur.

  • Generic utility functions that fetch Ether and ERC20 balances, sign data, format Etherscan links, expose npm packages, etc.

  • A fully managed solution for sending transactions that abstracts away from common annoyances like estimating gas usage and fetching current gas prices.

Example Projects

Projects using web-webpacked include:

Open a PR to add your project to this list!


Script Tag

Include the minified bundle (820 KiB) in your source code:

<script src="js/web3Webpacked.min.js"></script>

This binds the library to the window as w3w.


If you'd like to roll your own webpack solution, you can use the npm package:

npm install web3-webpacked
const w3w = require('web3-webpacked')

In either case, to initialize the package:

window.addEventListener('load', () => {
  console.log('Initializing web3 upon page load.')

If you don't need web3 functionality immediately on page load, you can initialize the package later:

if (document.readyState === 'complete') {
  console.log('Initializing web3 after page load.')

See Config Options for more instructions on what to include in the optional config variable, or Usage to jump right in.

Config Options

The following options can be set in the config variable passed to initializeWeb3.


  • Object Up to five handlers triggered on various events.
    • noWeb3Handler: function() Triggered when no injected window.web3 instance was found. This means that the user's browser does not have web3 support. Will also be triggered if your code calls initializeWeb3 before web3 injection occurred (in which case you should re-read the Installation instructions).
    • web3Ready: function() Triggered when the web3js instance is available to be fetched with getWeb3js, and the current network/accounts can be fetched with the their respective getters.
    • web3ErrorHandler: function([error]) Triggered when there was an error communicating with the Ethereum blockchain.
    • web3NetworkChangeHandler: function([networkId, oldNetworkId]) Triggered on network changes.
    • web3AccountChangeHandler: function([account, oldAccount]) Triggered on default account changes.


  • Number The poll interval (in milliseconds). The current recommendation is to poll for account and network changes.


  • Array of Numbers Enforces that the injected web3 instance is connected to a particular network. If the detected network id is not in the passed list, web3ErrorHandler will be triggered with an UnsupportedEthereumNetworkError error, and web3 functionality will be removed. Supported network ids are: 1, 3, 4, and 42.

Default Values

The default config values are below. You are encouraged to customize these!

let config = {
  handlers: {
    // Prompt the user to e.g. install MetaMask or download Trust
    noWeb3Handler: () => {
      console.error('No web3 instance detected.')
    // Check blockchain-dependent data
    web3Ready: () => {
      console.log('web3 initialized.')
    // Notify the user of error, deal with unsupported networks
    web3ErrorHandler: (error) => {
      if ( === networkErrorName) {
      } else {
        console.error(`web3 Error: ${error}`)
    // Notify the user that they have switched networks, potentially re-instatiate smart contracts
    web3NetworkChangeHandler: (networkId, oldNetworkId) => {
      console.log(`Network switched from ${oldNetworkId} to ${networkId}.`)
    // Notify the user that they have switched accounts, update balances
    web3AccountChangeHandler: (account, oldAccount) => {
      if (account === null) {
        console.log('No account detected, a password unlock is likely required.')
      } else {
        console.log(`Primary account switched from ${oldAccount} to ${account}.`)
  pollTime: 1000, // 1 second
  supportedNetworks: [1, 3, 4, 42] // mainnet, ropsten, rinkeby, kovan


  • w3w.initializeWeb3([config]): Initialize web3 in your project. See above for more details.
  • w3w.getWeb3js(): Returns a web3js instance (web3@1.0.0-beta.34).
  • w3w.getAccount(): Returns the current default account.
  • w3w.getNetworkId(): Returns the current network id as a Number. Possible values: 1, 3, 4, or 42.
  • w3w.getNetworkName([networkId]): Returns the name of a network (defaults to the current network). Possible values: Mainnet, Ropsten, Rinkeby, or Kovan.
  • w3w.getNetworkType([networkId]): Returns the type of a network (defaults to the current network). Possible values: PoW or PoA.
  • w3w.getContract(ABI[, address, options]): Returns a web3js Contract object.
  • w3w.getBalance([account, format]): Returns the balance of an Ethereum address (defaults to the current account).
  • w3w.getERC20Balance([ERC20Address, account]): Returns the token balance of an Ethereum address (defaults to the personal account) for any ERC20. Decimals are read from the smart contract.
  • w3w.toDecimal(number, decimals): number must be a String. Returns a decimalized version of the number as a String. Helpful when converting e.g. token balances from their uint256 state in an Ethereum smart contract to actual balances.
  • w3w.fromDecimal(number, decimals): number must be a String. The opposite of w3w.toDecimal. Converts the number to an expanded form.
  • w3w.sendTransaction(method, handlers): An all-in-one function that manages the entire transaction sending flow. Ensures that function call won't fail given the current state of the network, that the sender has enough ether to cover the gas costs of the transaction, and calls handlers appropriately. handlers is an Object that must include an error handler, as well as optional transactionHash, receipt, and confirmation handlers. These correspond to emitted web3js events.
  • w3w.signPersonal(message): Signs a message with the current default account per this article. Returns the signing address, message hash, and signature. The returned signature is guaranteed to have originated from the returned address.
  • w3w.signTypedData(typedData): Signs typed data with the current default account per this article. Returns the signing address, message hash, and signature. The returned signature is guaranteed to have originated from the returned address.
  • w3w.etherscanFormat(type, data[, networkId]): Returns an Etherscan link to a given transaction, address, or token (defaults to the current network).
  • w3w.networkErrorName: The name of the error thrown when the injected web3 instance is on an unsupported network.
  • w3w.libraries.


  • To ensure that your code is accessing the most up-to-date variables, be sure not to hard code values like the web3js instance, the default account, the current networkId, etc. Instead, call functions like w3w.getWeb3js() on demand, whenever you need a web3js instance.

  • web3-webpacked is forced to be opinionated, and has integrated web3js in lieu of possible alternatives like ethjs. In the future, it's possible that two branches will be maintained, with web3js and ethjs compatibility respectively. There is also an argument to be made for letting users build web3-webpacked themselves with arbitrary versions of these web3 APIs (how exactly this would look is TBD). If any of this is of interest, please submit an issue with your ideas/comments.

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