以太坊Dapp开发通过web3.js调用智能合约
在dapp目录下创建一个工程sixtest
[root@ dapp]# express -e sixtest
我们在remix当中部署好的智能合约
pragma solidity ^0.4.22;
contract counter{
uint256 counter;
constructor() public{
counter = 1;
}
function getCounter()public view returns(uint256){
return counter;
}
function changeCounter(uint256 a) public{
counter += a;
}
}
进入到sixtest目录下进行npm install操作
我们还需要进行安装web3
npm install web3 -save
修改routes目录下的index.js
var express = require('express');
var router = express.Router();
var Web3 = require('web3');
var web3 = new Web3(new Web3.providers.HttpProvider('http://localhost:8545'));
web3.getAccounts().then(console.log);
/* GET home page. */
router.get('/', function(req, res, next) {
res.render('index', { title: 'Express' });
});
module.exports = router;
修改目录下的app.js文件 vim app.js
var createError = require('http-errors');
var express = require('express');
var path = require('path');
var cookieParser = require('cookie-parser');
var logger = require('morgan');
var indexRouter = require('./routes/index');
var usersRouter = require('./routes/users');
var app = express();
var ejs = require('ejs');
// view engine setup
app.set('views', path.join(__dirname, 'views'));
app.engine('.html',ejs.__express);
app.set('view engine', 'html');
//app.set('view engine', 'ejs');
app.use(logger('dev'));
app.use(express.json());
app.use(express.urlencoded({ extended: false }));
app.use(cookieParser());
app.use(express.static(path.join(__dirname, 'public')));
app.use('/', indexRouter);
app.use('/users', usersRouter);
// catch 404 and forward to error handler
app.use(function(req, res, next) {
next(createError(404));
});
// error handler
app.use(function(err, req, res, next) {
// set locals, only providing error in development
res.locals.message = err.message;
res.locals.error = req.app.get('env') === 'development' ? err : {};
// render the error page
res.status(err.status || 500);
res.render('error');
module.exports = app;
在sixtest目录下的views当中创建index.html文件，并且将index.ejs复制到其中。
<!DOCTYPE html>
<html>
<head>
<title><%= title %></title>
<link rel='stylesheet' href='/stylesheets/style.css' />
</head>
<body>
<h1><%= title %></h1>
<p>Welcome to <%= title %></p>
</body>
</html>
测试是否能成功
[root@ sixtest]# npm start
> [email protected] start
> node ./bin/www
[
'0x930518c17201051A2C9a820c242F205f87767f06',
'0x652945236a3d96e631f95c9373Fc5d0774Ae2e92',
'0xbf4f91f8D7cb564e6d016DDA6a65BC5eDbacf902',
'0xD79a65Dc80bE92625D739e7daC05a361D9BeaF9E',
'0x8544049B57803e0a190445F268Fb3e7A3D307cED',
'0xb1a518Ca38F9532230ae982703eEC3844249E772',
'0xb24aCF61a30bcb618da8e27E57eC5167892E21A1',
'0xf02cFF084d416CD89057a067385ee8312DB51022',
'0x52B8600BB62938Fc461006BdE4a3c34A2914c5A4',
'0xBc07537f4E016FB3341728390285D271fefB48ce'
]
证明成功连上web3.js
现在进一步修改routes当中的index.js文件
**当中的代码段来源于web3.js开发手册当中的web3.eth.Contract中的new contract 创建一个新的合约实例：
var myContract = new web3.eth.Contract([…], ’ ', {
from: ‘0x1234567890123456789012345678901234567891’, // default from address
gasPrice: ‘20000000000’ // default gas price in wei, 20 gwei in this case
});
第一个[…]参数是智能合约的ABI，也就是下图当中的内容
第二个参数 ’ ’ 是你部署合约的地址 就是上一节以太坊Dapp开发通过web3.js部署合约当中最后的Contract address。
ar express = require('express');
var router = express.Router();
var Web3 = require('web3');
var web3 = new Web3(new Web3.providers.HttpProvider('http://localhost:8545'));
// web3.eth.getAccounts().then(console.log);
**var myContract = new web3.eth.Contract([
{
"constant": false,
"inputs": [
{
"name": "a",
"type": "uint256"
}
],
"name": "changeCounter",
"outputs": [],
"payable": false,
"stateMutability": "nonpayable",
"type": "function"
},
{
"inputs": [],
"payable": false,
"stateMutability": "nonpayable",
"type": "constructor"
},
{
"constant": true,
"inputs": [],
"name": "getCounter",
"outputs": [
{
"name": "",
"type": "uint256"
}
],
"payable": false,
"stateMutability": "view",
"type": "function"
}
], '0x2247fdbC867ab4A6fb85787Daa0c12B9aB27FB60');**
//myContract.methods.getCounter().call({from: '0x652945236a3d96e631f95c9373Fc5d0774Ae2e92'}, function(error, result){
// console.log("counter:",result);
//});
var init_counter = 0;
var current_counter = 0;
myContract.methods.getCounter().call().then(function(counter){
console.log('init counter:',counter);
init_counter = counter;
});
/* GET home page. */
router.get('/', function(req, res, next) {
myContract.methods.changeCounter(5).send({from: '0x652945236a3d96e631f95c9373Fc5d0774Ae2e92'})
.then(function(){
myContract.methods.getCounter().call().then(function(counter){
console.log('current counter:',counter);
current_counter = counter;
res.render('index', {init:init_counter,current:current_counter });
});
});
});
module.exports = router;
接下来我们来修改views当中的index.html
<!DOCTYPE html>
<html>
<head>
<title>调用智能合约</title>
<link rel='stylesheet' href='/stylesheets/style.css' />
</head>
<body>
<h1>init:<%= init%></h1>
<h1>current:<%= current%></h1>
</body>
</html>
最后我们来看一下效果
在sixtest目录下运行npm start命令
出现以下结果
[root@ sixtest]# npm start
> [email protected] start
> node ./bin/www
init counter: 1
此时在浏览器中打开http://127.0.0.1:3000
此时也会出现我们的current
[root@ sixtest]# npm start
> [email protected] start
> node ./bin/www
init counter: 1
current counter: 6
GET / 200 208.813 ms - 211
GET /stylesheets/style.css 200 32.996 ms - 111