web3.js 智能合约读函数基础教程文档

收录于 2023-04-20 00:10:05 · بالعربية · English · Español · हिंदीName · 日本語 · Русский язык · 中文繁體

智能合约对象的 methods属性下，包含了对应智能合约的所有函数。要调用智能合约中的某个函数，例如 myFunction()，可以使用 contract.methods.myFunction()的方式调用。
注意 这里调用方法只能调用读操作函数，不能调用写操作函数，写操作函数会改变区块链状态，调用写函数被视为交易。
继续上一章中的示例，我们已经创建了OmiseGo通证智能合约的Javascript对象。
由于这个智能合约实现了ERC-20标准，应该已经实现了这些函数： totalSupply()、 name()、 symbol()和 balanceOf()。
可以调用这些函数，如下所示:
查看现有OmiseGo通证的总供应量: 
contract.methods.totalSupply().call((err, result) => { console.log(result) })
// > 140245398245132780789239631
查看OmiseGo通证的名称: 
contract.methods.name().call((err, result) => { console.log(result) })
// > OMGToken
查看OmiseGo通证的标志: 
contract.methods.symbol().call((err, result) => { console.log(result) })
// > OMG
查看给定账户的余额
查看一下这个地址 0xd26114cd6EE289AccF82350c8d8487fedB8A0C07的OmiseGo通证余额情况。 
contract.methods.balanceOf('0xd26114cd6EE289AccF82350c8d8487fedB8A0C07').call((err, result) => { console.log(result) })
// > 22620364140612904305860

小结

下面是代码小结 
const Web3 = require('web3')
const rpcURL = '' // Your RCP URL goes here
const web3 = new Web3(rpcURL)
const abi = [{"constant":true,"inputs":[],"name":"mintingFinished","outputs":[{"name":"","type":"bool"}],"payable":false,"type":"function"},{"constant":true,"inputs":[],"name":"name","outputs":[{"name":"","type":"string"}],"payable":false,"type":"function"},{"constant":false,"inputs":[{"name":"_spender","type":"address"},{"name":"_value","type":"uint256"}],"name":"approve","outputs":[],"payable":false,"type":"function"},{"constant":true,"inputs":[],"name":"totalSupply","outputs":[{"name":"","type":"uint256"}],"payable":false,"type":"function"},{"constant":false,"inputs":[{"name":"_from","type":"address"},{"name":"_to","type":"address"},{"name":"_value","type":"uint256"}],"name":"transferFrom","outputs":[],"payable":false,"type":"function"},{"constant":true,"inputs":[],"name":"decimals","outputs":[{"name":"","type":"uint256"}],"payable":false,"type":"function"},{"constant":false,"inputs":[],"name":"unpause","outputs":[{"name":"","type":"bool"}],"payable":false,"type":"function"},{"constant":false,"inputs":[{"name":"_to","type":"address"},{"name":"_amount","type":"uint256"}],"name":"mint","outputs":[{"name":"","type":"bool"}],"payable":false,"type":"function"},{"constant":true,"inputs":[],"name":"paused","outputs":[{"name":"","type":"bool"}],"payable":false,"type":"function"},{"constant":true,"inputs":[{"name":"_owner","type":"address"}],"name":"balanceOf","outputs":[{"name":"balance","type":"uint256"}],"payable":false,"type":"function"},{"constant":false,"inputs":[],"name":"finishMinting","outputs":[{"name":"","type":"bool"}],"payable":false,"type":"function"},{"constant":false,"inputs":[],"name":"pause","outputs":[{"name":"","type":"bool"}],"payable":false,"type":"function"},{"constant":true,"inputs":[],"name":"owner","outputs":[{"name":"","type":"address"}],"payable":false,"type":"function"},{"constant":true,"inputs":[],"name":"symbol","outputs":[{"name":"","type":"string"}],"payable":false,"type":"function"},{"constant":false,"inputs":[{"name":"_to","type":"address"},{"name":"_value","type":"uint256"}],"name":"transfer","outputs":[],"payable":false,"type":"function"},{"constant":false,"inputs":[{"name":"_to","type":"address"},{"name":"_amount","type":"uint256"},{"name":"_releaseTime","type":"uint256"}],"name":"mintTimelocked","outputs":[{"name":"","type":"address"}],"payable":false,"type":"function"},{"constant":true,"inputs":[{"name":"_owner","type":"address"},{"name":"_spender","type":"address"}],"name":"allowance","outputs":[{"name":"remaining","type":"uint256"}],"payable":false,"type":"function"},{"constant":false,"inputs":[{"name":"newOwner","type":"address"}],"name":"transferOwnership","outputs":[],"payable":false,"type":"function"},{"anonymous":false,"inputs":[{"indexed":true,"name":"to","type":"address"},{"indexed":false,"name":"value","type":"uint256"}],"name":"Mint","type":"event"},{"anonymous":false,"inputs":[],"name":"MintFinished","type":"event"},{"anonymous":false,"inputs":[],"name":"Pause","type":"event"},{"anonymous":false,"inputs":[],"name":"Unpause","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"name":"owner","type":"address"},{"indexed":true,"name":"spender","type":"address"},{"indexed":false,"name":"value","type":"uint256"}],"name":"Approval","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"name":"from","type":"address"},{"indexed":true,"name":"to","type":"address"},{"indexed":false,"name":"value","type":"uint256"}],"name":"Transfer","type":"event"}]
const address = '0xd26114cd6EE289AccF82350c8d8487fedB8A0C07'
const contract = new web3.eth.Contract(abi, address)
contract.methods.totalSupply().call((err, result) => { console.log(result) })
contract.methods.name().call((err, result) => { console.log(result) })
contract.methods.symbol().call((err, result) => { console.log(result) })
contract.methods.balanceOf('0xd26114cd6EE289AccF82350c8d8487fedB8A0C07').call((err, result) => { console.log(result) })