web3js调用已部署智能合约的function

[h1]简介与环境[/h1][h2]简介[/h2]

web3.js是以太坊提供的一个Javascript库，它封装了以太坊的JSON RPC API、IPC调用，提供了一系列与以太坊区块链交互的J对象和函数。几乎囊括JSON RP的API，还可以编译和部署智能合约以及调用智能合约等，其中最重要的就是与智能合约交互的JS对象及函数。

[h2]开发环境[/h2]

macos操作系统
nodejs 8.9.4
npm 5.6.0

[h1]调用智能合约[/h1]首先需要使用Solidity编写智能合约，最简单的合约如下，不与区块发生联系：

pragma solidity ^0.4.2; contract hello { function hello() public { } function say() constant public returns (string) { return "Hello World!"; } }

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注：Solidity在线编译环境地址点我
编译后会产生很多不同的东西，部分如下：
WEB3DEPLOY：

var helloContract = web3.eth.contract([{"constant":true,"inputs":[],"name":"say","outputs":[{"name":"","type":"string"}],"payable":false,"type":"function","stateMutability":"view"},{"inputs":[],"payable":false,"type":"constructor","stateMutability":"nonpayable"}]);var hello = helloContract.new( { from: web3.eth.accounts[0], data: '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', gas: '4700000' }, function (e, contract){ console.log(e, contract); if (typeof contract.address !== 'undefined') { console.log('Contract mined! address: ' + contract.address + ' transactionHash: ' + contract.transactionHash); } })

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ABI（后面会用到）：

[ { "constant": true, "inputs": [], "name": "say", "outputs": [ { "name": "", "type": "string" } ], "payable": false, "type": "function", "stateMutability": "view" }, { "inputs": [], "payable": false, "type": "constructor", "stateMutability": "nonpayable" }]

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创建一个test.js，内容如下：

// 引入依赖模块var express = require("express")var Web3 = require("web3")var net = require("net")var http = require("http")var web3;// 创建web3对象并连接到以太坊节点if (typeof web3 !== 'undefined') { web3 = new Web3(web3.currentProvider);} else { // set the provider you want from Web3.providers web3 = new Web3(new Web3.providers.HttpProvider("http://192.168.53.60:8545"));}// 合约ABIvar abi = [{"constant":true,"inputs":[],"name":"say","outputs":[{"name":"","type":"string"}],"payable":false,"stateMutability":"view","type":"function"},{"inputs":[],"payable":false,"stateMutability":"nonpayable","type":"constructor"}];// 合约地址var address = "0xf77976c9a552f2934d3694c38fbd057ae803ef45";// 通过ABI和地址获取已部署的合约对象var helloContract = new web3.eth.Contract(abi,address);http.createServer(function (request, response) { // 调用智能合约方法 var helloResult = helloContract.methods.say().call().then(function(result){ console.log("返回值:" + result); // 发送 HTTP 头部 // HTTP 状态值: 200 : OK // 内容类型: text/plain response.writeHead(200, {'Content-Type': 'text/plain'}); // 发送响应数据 response.end(result);}); }).listen(8888);// 终端打印如下信息console.log('Server running at http://127.0.0.1:8888/');

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启动之前应该先加载test.js所依赖的模块：

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运行

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终端打印出"Server running at http://127.0.0.1:8888" 时即可访问"http://127.0.0.1:8888" ，网页会返回"Hello World"！