feat: add web3js paymaster dapp tutorial

content/tutorials/web3js-paymaster-tutorial/10.index.md

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+---
+title: Building a dApp with Stablecoin Gas Payments using Web3.js
+description: Learn how to build a decentralized application that enables users to pay transaction gas fees using stablecoins instead of ETH on ZKSync.
+---
+
+Build a decentralized application that allows users to pay transaction gas fees using stablecoins instead of ETH on ZKSync.
+
+## Prerequisites
+
+- Node.js v14 or later
+- Basic knowledge of React and TypeScript
+- Understanding of Web3 concepts
+- MetaMask wallet
+- Basic understanding of smart contracts
+
+## Project Setup
+
+  1. Create a new React TypeScript project:
+
+      ```bash{copy}
+      npx create-react-app zksync-paymaster-demo --template typescript
+      cd zksync-paymaster-demo
+      ```
+
+  2. Install required dependencies:
+
+      ```bash{copy}
+      npm install web3 web3-plugin-zksync zksync-web3-contract-paymaster-plugin
+      ```
+
+## Smart Contract Setup
+
+::callout{icon="i-ph-info-bold"}
+First, let's set up our contract addresses and ABIs in a constants file. You'll need these for interacting with the smart contracts.
+::
+
+Store your contract addresses and ABIs in a constants file:
+
+```typescript{copy}
+export const MOCK_USDT_ADDRESS = "0xff68f7561562C1F24A317d939B46741F76c4Ef55";
+export const MOCK_USDT_PAYMASTER_ADDRESS = "0xfA7Adc05E56893df8ecE1F63E4dB1db7767146f4";
+export const STORE_CONTRACT_ADDRESS = "0xEc969112DB5440c954CB60B4Bbd1159673eeE4C3";
+
+export const MOCK_USDT_ADDRESS = "0xff68f7561562C1F24A317d939B46741F76c4Ef55";
+export const MOCK_USDT_PAYMASTER_ADDRESS = "0xfA7Adc05E56893df8ecE1F63E4dB1db7767146f4";
+export const STORE_CONTRACT_ADDRESS = "0xEc969112DB5440c954CB60B4Bbd1159673eeE4C3";
+
+// Store Contract ABI
+export const STORE_CONTRACT_ABI = [
+  {
+    "inputs": [
+      {
+        "internalType": "uint256",
+        "name": "_productId",
+        "type": "uint256"
+      },
+      {
+        "internalType": "uint256",
+        "name": "_quantity",
+        "type": "uint256"
+      }
+    ],
+    "name": "purchaseProduct",
+    "outputs": [],
+    "stateMutability": "nonpayable",
+    "type": "function"
+  },
+ 
+];
+
+// Stablecoin (MOCK USDT) ABI
+export const STABLECOIN_ABI = [
+  
+  {
+    "inputs": [
+      {
+        "internalType": "address",
+        "name": "spender",
+        "type": "address"
+      },
+      {
+        "internalType": "uint256",
+        "name": "amount",
+        "type": "uint256"
+      }
+    ],
+    "name": "approve",
+    "outputs": [
+      {
+        "internalType": "bool",
+        "name": "",
+        "type": "bool"
+      }
+    ],
+    "stateMutability": "nonpayable",
+    "type": "function"
+  },
+  
+];
+```
+
+## Paymaster Integration
+
+### Understanding Paymasters in ZKSync
+
+::callout{icon="i-ph-lightbulb-bold"}
+Before diving into the implementation, it's important to understand what a Paymaster is and how it works in ZKSync.
+::
+
+A Paymaster is a smart contract in ZKSync that enables gas abstraction - allowing users to pay transaction fees with tokens other than ETH.
+This is a powerful feature that improves user experience by:
+
+- Letting users pay gas fees in ERC20 tokens
+- Enabling sponsored transactions where a third party pays the gas
+- Supporting more complex gas payment scenarios
+
+In this tutorial we are using a custom made paymaster which accepts a custom token as referenced above:
+`MOCK_USDT_PAYMASTER_ADDRESS` and `MOCK_USDT_ADDRESS`. The paymaster contract address must be supplied to the `zksync-web3-contract-paymaster-plugin`.
+A comprehensive guide on creating a custom ERC20 paymaster can be found in the [ZKSync ERC20 Paymaster Tutorial](https://code.ZKSync.io/tutorials/erc20-paymaster).
+
+1. Create a custom hook for Paymaster interactions
+2. Set up Web3 and plugin initialization
+3. Implement contract interaction methods
+
+### Implementation
+
+1. Create a custom hook for Paymaster interactions:
+
+    ```typescript{copy}
+    import { useState, useEffect, useCallback } from 'react';
+    import Web3 from 'web3';
+    import { getPaymasterParams, types, Web3ZKSyncL2, ZKSyncPlugin } from 'web3-plugin-zksync';
+    import ZKSyncContractPaymasterPlugin from "zksync-web3-contract-paymaster-plugin";
+    import { MOCK_USDT_ADDRESS } from './constants';
+
+    const usePaymasterAsync = (contractAddress: string, contractAbi: any, _paymasterAddress?: string) => {
+        // Note: _paymasterAddress is optional - if not provided, the plugin will use testnet paymaster
+        const [web3, setWeb3] = useState<Web3>();
+        const [plugin, setPlugin] = useState<ZKSyncContractPaymasterPlugin>();
+
+        // Initialize Web3 and register the required plugins
+        useEffect(() => {
+            const initializeWeb3 = async () => {
+                if (typeof window.ethereum !== 'undefined') {
+                    // Create Web3 instance
+                    const web3 = new Web3(window.ethereum);
+                    
+                    // Initialize ZKSync L2 provider for Sepolia testnet
+                    const l2 = Web3ZKSyncL2.initWithDefaultProvider(types.Network.Sepolia);
+                    
+                    // Create instance of the Paymaster plugin
+                    const plugin = new ZKSyncContractPaymasterPlugin(window.ethereum);
+                    
+                    // Register both plugins with Web3
+                    web3.registerPlugin(plugin);
+                    web3.registerPlugin(new ZKSyncPlugin(l2));
+                    
+                    setPlugin(plugin);
+                    setWeb3(web3);
+                }
+            };
+
+            initializeWeb3();
+        }, []);
+
+        // This function handles contract interactions with Paymaster integration
+        const writeContractWithPaymaster = useCallback(async (
+            { functionName, args }: { functionName: string; args: any[] }
+        ) => {
+            if (!web3 || !plugin) return;
+            
+            return await plugin.write(contractAddress, contractAbi, {
+                methodName: functionName,
+                args: args,
+                from: await web3.eth.getAccounts().then(a => a[0]),
+                customData: {
+                    // Gas per pubdata is a ZKSync-specific parameter
+                    gasPerPubdata: 50000,
+                    // Configure Paymaster parameters for gas abstraction
+                    paymasterParams: getPaymasterParams(_paymasterAddress, {
+                        type: "ApprovalBased",
+                        minimalAllowance: 10,
+                        token: MOCK_USDT_ADDRESS,
+                        innerInput: new Uint8Array(),
+                    })
+                }
+            });
+        }, [web3, plugin, contractAddress]);
+
+        return { writeContractWithPaymaster };
+    };
+    ```
+
+    The `usePaymasterAsync` hook does several important things:
+
+    • Initializes Web3 with ZKSync plugins
+
+    • Provides a function to interact with any smart contract while using the Paymaster  
+
+    • Handles the configuration of Paymaster parameters for gas fee abstraction
+
+2. Implement the purchase function with Paymaster support:
+
+  This example shows how to use the Paymaster hook with any smart contract.
+  In this case, we're using a marketplace contract that takes a
+  product ID and quantity, but you can adapt this pattern for any contract function:
+
+```typescript{copy}
+const buyProductWithPayMaster = async (product: Product, itemQty: number) => {
+    try {
+        // IMPORTANT: First approve the spending of tokens
+        // This is required for any ERC20 token interaction
+        const approvalTx = await approveWithPaymasterAsync(
+            { 
+                functionName: 'approve',
+                args: [STORE_CONTRACT_ADDRESS, product.price]
+            }
+        );
+        
+        // Wait for approval transaction to be confirmed
+        await approvalTx.wait();
+
+        // Then make the actual contract call
+        // This could be any function on any contract
+        const tx = await buyWithPaymasterAsync(
+            {
+                functionName: 'purchaseProduct', // Your contract function name
+                args: [product.id, itemQty]     // Your function arguments
+            }
+        );
+        
+        return { tx, product };
+    } catch (error) {
+        console.error('Error buying product with Paymaster', error);
+        throw error;
+    }
+};
+
+// Example of how this is used in a component
+const Products = ({ account, web3 }) => {
+    // Initialize the Paymaster hooks for both token and marketplace contracts
+    const { writeContractWithPaymaster: approveWithPaymasterAsync } = usePaymasterAsync(
+        MOCK_USDT_ADDRESS,    // Token contract
+        STABLECOIN_ABI, 
+        MOCK_USDT_PAYMASTER_ADDRESS
+    );
+    
+    const { writeContractWithPaymaster: buyWithPaymasterAsync } = usePaymasterAsync(
+        STORE_CONTRACT_ADDRESS,  // Your contract
+        STORE_CONTRACT_ABI, 
+        MOCK_USDT_PAYMASTER_ADDRESS
+    );
+
+    // Function to handle the purchase
+    async function buy(product: Product, quantity: number) {
+        if (!web3 || !account) {
+            toast.error('Wallet not connected');
+            return;
+        }
+
+        const id = toast.loading(`Purchasing ${product.name}... and paying gas fees with MOCK_USDT`);
+        try {
+            const val = await buyProductWithPayMaster(product, quantity);
+            if (!val) return;
+            
+            const { tx } = val;
+            toast.success(`Purchase successful. Gas paid with MOCK_USDT`, { id });
+        } catch (error) {
+            toast.error('Error purchasing product: ' + error, { id });
+        }
+    }
+
+    return (
+        // Your UI components
+    );
+};
+```
+
+::callout{icon="i-ph-list-checks-bold"}
+Here are the key points to remember when implementing Paymaster functionality:
+::
+
+1. **Token Approval**: Before any ERC20 token transaction, you must approve the spending amount. This is standard for all ERC20 tokens.
+
+2. **Contract Interaction**: The example shows a purchase function, but you can use this pattern with any smart contract function. Just modify:
+   - The contract address
+   - The contract ABI
+   - The function name
+   - The function arguments
+
+3. **Gas Payment**: The Paymaster handles converting your token payment into gas fees automatically.
+
+## Conclusion
+
+This tutorial demonstrated how to build a dApp that leverages ZKSync's Paymaster feature to enable stablecoin gas payments. The key components are:
+
+- Integration with ZKSync's L2 network using the Paymaster plugin
+- Smart contract interactions for token approvals and purchases
+- User interface for seamless interaction
+
+::callout{icon="i-ph-arrow-right-bold"}
+You can view a live demo of this implementation at [Web3js ZKSync Plugin Demo](https://web3js-ZKSync-plugin.vercel.app/).
+::
+
+::alert{type="success"}
+Congratulations! You've built a dApp that uses ZKSync's Paymaster feature to enable stablecoin gas payments.
+::

content/tutorials/web3js-paymaster-tutorial/_dir.yml

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+title: Building a ZKSync dApp with Stablecoin Gas Payments using Web3.js
+authors:
+  - name: Jovells
+    image: https://avatars.githubusercontent.com/u/100000000?v=4
+    twitter: https://twitter.com/jovells
+    github: https://github.com/jovells
+tags:
+  - web3.js
+  - paymaster
+  - gas-abstraction
+  - stablecoin
+  - react
+  - typescript
+level: intermediate
+duration: 45 minutes
+github_repo: https://github.com/Jovells/ZKSync-web3js-paymaster-demo
+summary: |
+  Learn how to build a dApp that allows users to pay transaction gas fees using stablecoins instead of ETH on ZKSync. 
+  This tutorial uses Web3.js and ZKSync's Paymaster feature to implement gas abstraction.
+description: |
+  This comprehensive guide walks through creating a decentralized application that leverages ZKSync's Paymaster feature 
+  for stablecoin gas payments. You'll learn how to integrate Web3.js with ZKSync plugins, implement smart contract 
+  interactions, and create a user interface for seamless gas abstraction.
+what_you_will_learn:
+  - How to integrate Web3.js with ZKSync plugins
+  - How to implement smart contract interactions
+  - How to create a user interface for seamless gas abstraction
+updated: 2024-12-21
+tools:
+  - Web3.js
+  - React
+  - MetaMask