區塊鏈 14 | 自製一個以太坊私有鏈（三）

使用Web3.js取得以太坊私有鏈上的資料、部署智能合約

Photo by Brigitte Tohm on Unsplash

web3.js 是Ethereum 開發的JavaScript API

要運行web3.js的話用node最方便，所以先來建置一個簡單的node 專案

Desktop$ mkdir web3_project
Desktop$ cd web3_project
Desktop web3_project$ npm init

在專案中安裝web3.js模組

$ npm install web3 --save

• Web3.js官方文件 : Ethereum API

在專案根目錄直接新增一個 index.js檔案，填入下列 code：

const Web3 = require('web3');
// connect to ethereum node
const ethereumUri = 'http://localhost:8545'; // port 預設8545，可以另行設定
const web3 = new Web3(ethereumUri);
// 取得帳戶資訊
 web3.eth.getAccounts().then(console.log);

執行index.js

$ node index.js

如果有返回一串0x開頭的數值像這樣：

['0xD452eC5f19669c220c2be79Fa0Cf69427dC3dbB7']

表示與私有鏈連結成功！

其他web3.js 的方法

• 取得現在區塊數，回傳區塊號碼(int)

web3.eth.getBlockNumber().then(console.log);
>2744

• 取得某一帳戶的餘額，回傳餘額(int)

web3.eth.getBalance("0xD452eC5f19669c220c2be79Fa0Cf69427dC3dbB7").then(console.log);
>"1000000000000"

• 取得某一區塊資訊: 需帶入 “區塊號碼” 或是 “區塊hash值”，回傳區塊資訊(object)

web3.eth.getBlock(2744).then(console.log);
>{
"number": 2744,
"hash": "0xef95f2f1ed3ca60b048b4bf67cde2195961e0bba6f70bcbea9a2c4e133e34b46",
"parentHash": "0x2302e1c0b972d00932deb5dab9eb2982f570597d9d42504c05d9c2147eaf9c88",
"nonce": "0xfb6e1a62d119228b",
"sha3Uncles": "0x1dcc4de8dec75d7aab85b567b6ccd41ad312451b948a7413f0a142fd40d49347",
"logsBloom": "0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000",
"transactionsRoot": "0x3a1b03875115b79539e5bd33fb00d8f7b7cd61929d5a3c574f507b8acf415bee",
"stateRoot": "0xf1133199d44695dfa8fd1bcfe424d82854b5cebef75bddd7e40ea94cda515bcb",
"miner": "0x8888f1f195afa192cfee860698584c030f4c9db1",
"difficulty": "21345678965432",
"totalDifficulty": "324567845321",
"size": 616,
"extraData": "0x",
"gasLimit": 3141592,
"gasUsed": 21662,
"timestamp": 1429287689,
"transactions": [
"0x9fc76417374aa880d4449a1f7f31ec597f00b1f6f3dd2d66f4c9c6c445836d8b"
],
"uncles": []
}

• 解鎖帳戶(unlock account)

web3.eth.personal.unlockAccount("0x11f4d0A3c12e86B4b5F39B213F7E19D048276DAe", "test password!", 600).then(console.log("Account unlocked!"));

接下來學習如何使用Web3.js部署智能合約

使用Web3.js部署智能合約

1. 編譯智能合約，取得編譯好的合約json檔

** 智能合約的編譯是使用truffle 框架另外做的，以下是一個簡單的智能合約範例：

pragma solidity ^0.5.16;
contract SimpleStorage {
    uint storedData;
    
    function set(uint x) public {
        storedData = x;
    }
    
    function get() view public returns (uint) {
        return storedData;
    }
}

2. 在剛剛的node專案中(index.js)，引入編譯好的智能合約(json)檔案

const json = require(“contracts/SimpleStorage.json”);

3. 部署合約

// 建立新合約的Interface
const myContract = new web3.eth.Contract(json.abi)
// 部署合約
myContract.deploy({
    data: json.bytecode
})
.send({
    from: accounts[0],
    gas: 1500000,
    gasPrice: '30000000000000'
})
.then(function(newContractInstance){
    contAddress = newContractInstance.options.address
    console.log(newContractInstance.options.address) 
    // instance with the new contract address
});

如果回傳合約地址表示成功將合約部署上鏈了！

呼叫智能合約的方法修改資料

// 首先要找到那張智能合約，一樣要先建立一個新的合約的Interface
const myContract = new web3.eth.Contract(json.abi, contAddress, {from: accounts[0]})

// 呼叫方法: 修改鏈上資料的
result = myContract.methods.set(123456789).send({from: accounts[0]})

// 呼叫方法: 取出鏈上資料
result1 = await myContract.methods.get().call();
console.log('result1 '+ result1)   // 123456789

參考

• 查看完整程式碼【github web3js blockchain】