> ## Documentation Index
> Fetch the complete documentation index at: https://docs.celo.org/llms.txt
> Use this file to discover all available pages before exploring further.

# Web3.js

## Web3.js (deprecated)

<Note>
  Web3.js has been sunset in 2024. Please consider using [thirdweb](https://thirdweb.com/?utm_source=celo\&utm_medium=documentation\&utm_campaign=chain_docs) or viem for your project.
</Note>

Web3.js was established in 2014, making it the oldest web3 library. With extensive documentation, an active community and modular design, Web3.js is powerful and easy-to-use. It has *support for Celo features (specifically **[Fee Abstraction](/build-on-celo/fee-abstraction/overview)** via plugins since version 4.13.1*.

To learn more about building with Web3.js, check out their [docs](https://docs.web3js.org/) as they have excellent examples of how to use it in your project.

### Fee Abstraction with Web3.js

[Fee Abstraction](/build-on-celo/fee-abstraction/overview) on Celo enables the use of stablecoins like cUSD, USDT and USDC as gas tokens.

#### Requirements

* Web3.js v. > 4.13.1

#### Install the Celo Web3.js Plugin

For Celo' specific features like [Fee Abstraction](/build-on-celo/fee-abstraction/overview) transactions you need to install `@celo/web3-plugin-transaction-types` as well as `web3@4.13.1` or higher. This also adds utils like `getCoreContractAddress` for fetching core contract address from onchain registry. This is useful to get the stablecoin addresses you are planning to use programmatically. Make sure they are listed in the [**FeeCurrencyDirectory.sol**](/contracts/core-contracts).

<CodeGroup>
  ```bash yarn theme={null}
  yarn add @celo/web3-plugin-transaction-types web3
  ```

  ```bash npm theme={null}
  npm install @celo/web3-plugin-transaction-types web3
  ```
</CodeGroup>

Now `web3.celo` is available and `web3.eth` is "celo-aware". "aware" means that if the tx has the `feeCurrency` param, calling `eth.sendTransaction` will use the celo cip64 serializer and be able to recognize the fee currency.

Here an example on how to use "feeCurrency" with cEUR.

```ts theme={null}
// see web3 docs for more info on setup

import { Web3 } from "web3";
import { CeloTransactionTypesPlugin } from "@celo/web3-plugin-transaction-types";

const web3 = new Web3("http://127.0.0.1:8545");
web3.registerPlugin(new CeloTransactionTypesPlugin());

// Now `web3.celo` is available and `web3.eth` is celo-aware. 
// Get all StableToken Addresses through the getCoreContractAddress
const cEUR = await web3.celo.getCoreContractAddress("StableTokenEUR");
const txData = {
  from: "0x123...",
  to: "0x456...",
  value: 123n,
  // find the list of accepted tokens in the Fee Abstraction documentation
  feeCurrency: cEUR, // optional
};
await web3.celo.populateTransaction(txData);
const tx = await web3.eth.sendTransaction(txData);
```

## Gas Price

When paying for transaction with an alternate feeCurrency token it is **important** to know the price of gas denominated in that token. You can use `web3.celo.populateTransaction` to make sure `maxPriorityFeePerGas`, `maxFeePerGas`, and `gas` are filled properly.

```ts theme={null}
await web3.celo.populateTransaction(txData);
```

You can find more examples in the [github repository readme](https://github.com/celo-org/web3-plugin-transaction-types).