Javascript 仅当值不存在时才向对象添加新数组项

我编写了以下代码来存储数据检索值并将数据存储到对象中：

var contract = new web3.eth.Contract(contractAbi, contractAddress);
var accounts = {};
var balance = {};


// Crawl the Chain from the Contract Deployment Date till the latest block
contract.getPastEvents(
    'Transfer',
    {
      fromBlock: 8437000,
      toBlock: 'latest'
    },(error, events) => { 

    if (!error){
      var obj=JSON.parse(JSON.stringify(events));

      for (const [key, val] of Object.entries(obj)) {
        accounts[val.blockNumber] = {
            _from: val.returnValues._from,
            _to: val.returnValues._to,
            _value: parseInt(val.returnValues._value, 10)
            // _value: val.returnValues._value
        };
    }

    }
    else {
      console.log(error)
}

Object.entries(accounts).forEach(([key, val]) => console.log(key, val)); 

})

这工作正常，其输出为：

8441134 { _from: '0x34872874b65E12408eC0265E9cf0a35FA6c8D13E',
  _to: '0x39BC998bD7DC71885661B1062CC2baa9fbe94F45',
  _value: 76470000000000000000 }
8441135 { _from: '0x85C5c26DC2aF5546341Fc1988B9d178148b4838B',
  _to: '0x2E642b8D59B45a1D8c5aEf716A84FF44ea665914',
  _value: 947018889517274100000 }
8441142 { _from: '0xda7C4aAb9bb74710498485ed01CB4D521f7b4456',
  _to: '0x24fa98CA3aB52D8CF562B641AbC4b12861e991Cf',
  _value: 321279880100000000000 }
8441157 { _from: '0x46340b20830761efd32832A74d7169B29FEB9758',
  _to: '0xeE7D76D5B00A10B49e37a9e26a7678be1EE607F4',
  _value: 29500000000000000000 }
8441167 { _from: '0x2baa435Ca4B9dE4a135cAE11f4c04C4a1d334089',
  _to: '0x9fa7f05C9AaE89752fa9273CFAcADF602657599d',
  _value: 1.5043600286e+21 }

我想将其转换为一种格式，其中每个帐户（_to和_from）都将作为帐户添加到块上的索引中，即

// The _to and _from fields become account entries
8441142 { Accounts: '0xda7C4aAb9bb74710498485ed01CB4D521f7b4456',
                    '0x24fa98CA3aB52D8CF562B641AbC4b12861e991Cf'}
// Add accounts that did not previously exist, ignore ones already in here
8441157 { Accounts: 0xda7C4aAb9bb74710498485ed01CB4D521f7b4456',
                  '0x24fa98CA3aB52D8CF562B641AbC4b12861e991Cf', '0x46340b20830761efd32832A74d7169B29FEB9758','0xeE7D76D5B00A10B49e37a9e26a7678be1EE607F4'}
// Add accounts that did not previously exist, ignore ones already in here
8441167 { Accounts: '0x2baa435Ca4B9dE4a135cAE11f4c04C4a1d334089','0x9fa7f05C9AaE89752fa9273CFAcADF602657599d'}

---

我希望有人能指点我如何有效地做到这一点。

在循环之外使用一个变量来保存上一个块中的帐户列表。制作一份副本，并将新帐户推送到该副本上

  let last_accounts = [];
  for (const [key, {blockNumber, returnValues: {_from, _to}}] of Object.entries(obj)) {
    let these_accounts = last_accounts.slice(); // copy accounts from previous block
    if (!these_accounts.includes(_from)) {
        these_accounts.push(_from);
    }
    if (!these_accounts.includes(_to)) {
        these_accounts.push(_to);
    }
    accounts[blockNumber] = {Accounts: these_accounts};
    last_accounts = these_accounts;
  }

---

所需的结果不是有效的对象。是否希望帐户的值成为数组？谢谢！这使我更接近我的目标，但我的问题可能不是很清楚。我希望每个新的块/索引是现有帐户+新帐户（如果它们不存在）的累积。非常感谢您的帮助我是否打算打印

账户

或

这些账户

？

这些账户

只是一个临时局部变量

accounts

是包含所有结果的全局变量。这是累积变量，可以根据需要进行累积<代码>账户[blockNumber]=账户[blockNumber]| |{账户：[]}意味着使用

accounts[blockNumber]

的值（如果它已经存在），否则用空数组将其初始化为该对象。哦，我想你是指以前对该循环调用的累积值。