在解决了其中包含嵌套承诺的承诺后执行代码

Question

我有如下js代码结构；

Promise_1.then(function(){
  for(){
    Promise2.then(function(){
      ...
    })
  }
}).then(
  Promise_3.then(function(){
    for(){
      Promise4.then(function(){
        ...
      })
    }
  })
).then(
  function(){
    // SOME CODE
  }
)

我想在上述承诺得到解决后执行一些代码。但是在上述承诺得到解决之前，SOME CODE 正在执行。我知道我可以在 setTimeout() 中附上一些代码，这将解决 SO 上其他答案所建议的问题，但我认为这不是一个好主意。我正在处理的实际代码如下；

user_xp = 0
connections_blocks.methods.get_deposit_blocks(current_email).call({
    from: new_web3.eth.Contract.defaultAccount
}, function (err, result) {
    deposit_blocks = result
    console.log(deposit_blocks)
    deposit_blocks = deposit_blocks.split(",")
    deposit_blocks.splice(0, 1)
    for (i_ in deposit_blocks) {
        console.log(deposit_blocks[i_])
        user_xp + new_web3.eth.getBlock(deposit_blocks[i_]).then(function (deposit_block) {
            user_xp = user_xp + deposit_block.gasUsed
            console.log(user_xp)
        })
    }
}).then(
    connections_blocks.methods.get_send_blocks(current_email).call({
        from: new_web3.eth.Contract.defaultAccount
    }, function (err, result) {
        send_blocks = result
        console.log(send_blocks)
        send_blocks = send_blocks.split(",")
        send_blocks.splice(0, 1)
        for (i_ = 0; i_ < send_blocks.length; i_ = i_ + 2) {
            console.log(send_blocks[i_])
            user_xp + new_web3.eth.getBlock(send_blocks[i_]).then(function (send_block) {
                user_xp = user_xp + send_block.gasUsed
                console.log(user_xp)
            })
        }
    })).then(
    setTimeout(function () {
        console.log(user_xp)
        xp = document.getElementById('xp')
        xp.innerHTML = "XP:" + user_xp
    },1000)
)

在上面的代码中，我只是使用 setTimeout() 来解决我的问题。但我希望代码仅在上述承诺得到解决时自动执行。有什么简单的方法可以在 JS w/o 中将 promises 放入函数中并使其更复杂。

更新

我正在使用以下 web3 的函数从 solidity 的智能合约中获取数据，这实际上是 returns 对数据的承诺 promiseValue

myContract.methods.myMethod([parameters).call(options,[callback])

Answer 1

我假设 Promise_1 和 Promise_3 的解析将等待回调完成。如果是这种情况，这应该有效。

user_xp = 0

connections_blocks.methods.get_deposit_blocks(current_email).call({
    from: new_web3.eth.Contract.defaultAccount
}, function (err, result) {
    deposit_blocks = result
    console.log(deposit_blocks)
    deposit_blocks = deposit_blocks.split(",")
    deposit_blocks.splice(0, 1)
    // array to hold the promises
    const subPromises = []
    for (i_ in deposit_blocks) {
        console.log(deposit_blocks[i_])
        subPromises.push(new_web3.eth.getBlock(deposit_blocks[i_]))
    }
    // waiting for all promises to resolve
    Promise.all(subPromises).then(function (deposit_block) {
        user_xp = user_xp + deposit_block.gasUsed
        console.log(user_xp)
    })
})
.then(
    connections_blocks.methods.get_send_blocks(current_email).call({
        from: new_web3.eth.Contract.defaultAccount
    }, function (err, result) {
        send_blocks = result
        console.log(send_blocks)
        send_blocks = send_blocks.split(",")
        send_blocks.splice(0, 1)
        const subPromises = []
        for (i_ = 0; i_ < send_blocks.length; i_ = i_ + 2) {
            console.log(send_blocks[i_])
            subPromises.push(
                new_web3.eth.getBlock(send_blocks[i_])
            )
        }
        Promise.all(subPromises).then(function (send_block) {
            user_xp = user_xp + send_block.gasUsed
            console.log(user_xp)
        })
    })
)
.then(function () {
    console.log(user_xp)
    xp = document.getElementById('xp')
    xp.innerHTML = "XP:" + user_xp
})

Answer 2

您的代码问题包括

.then 的参数必须是函数
如果你需要在循环中等待Promise，你需要将它们添加到一个数组中，然后使用promise.all等待它们全部被解决

尝试对您的 actual 代码进行以下更改 - 我假设在没有节点样式回调的情况下，函数 returns 解析为 result 将传递给节点样式回调（在此代码中删除）

（如果您稍等片刻，我会展平 promise 链 - 只是注意到它并没有达到预期的水平

user_xp = 0
return connections_blocks.methods.get_deposit_blocks(current_email).call({
    from: new_web3.eth.Contract.defaultAccount
})
.then(function (result) {
    var promises = []
    deposit_blocks = result
    console.log(deposit_blocks)
    deposit_blocks = deposit_blocks.split(",")
    deposit_blocks.splice(0, 1)
    for (i_ in deposit_blocks) {
        console.log(deposit_blocks[i_])
        promises.push(
            new_web3.eth.getBlock(deposit_blocks[i_]).then(function (deposit_block) {
                user_xp = user_xp + deposit_block.gasUsed
                console.log(user_xp)
            })
        )
    }
    return Promise.all(promises)
})
.then(function () {
    return connections_blocks.methods.get_send_blocks(current_email).call({
        from: new_web3.eth.Contract.defaultAccount
    })
})
.then(function (result) {
    var promises=[]
    send_blocks = result
    console.log(send_blocks)
    send_blocks = send_blocks.split(",")
    send_blocks.splice(0, 1)
    for (i_ = 0; i_ < send_blocks.length; i_ = i_ + 2) {
        console.log(send_blocks[i_])
        promises.push(
            new_web3.eth.getBlock(send_blocks[i_]).then(function (send_block) {
                user_xp = user_xp + send_block.gasUsed
                console.log(user_xp)
            })
        )
    }
    return Promise.all(promises)
})
.then(function () {
    console.log(user_xp)
    xp = document.getElementById('xp')
    xp.innerHTML = "XP:" + user_xp
})

作为补充"bonus"，相信代码可以简化为

return connections_blocks.methods.get_deposit_blocks(current_email).call({
    from: new_web3.eth.Contract.defaultAccount
})
.then(result => Promise.all(result.split(",").slice(1).map(deposit_block => new_web3.eth.getBlock(deposit_block)
    .then(deposit_block => deposit_block.gasUsed)
})
.then(gasUsed1Array => connections_blocks.methods.get_send_blocks(current_email).call({
        from: new_web3.eth.Contract.defaultAccount
    })
    .then(result => Promise.all(result.split(",").slice(1).filter((v, i) => !(i%2)).map(send_blocks => new_web3.eth.getBlock(send_block)
        .then(send_block => send_block.gasUsed)
    )))
    .then(gasUsed2Array => [...gasUsed1Array, ...gasUsed2Array])
)
.then(results => {
    user_xp = results.reduce((a, b) => a + b);
    console.log(user_xp)
    xp = document.getElementById('xp')
    xp.innerHTML = "XP:" + user_xp
})

在解决了其中包含嵌套承诺的承诺后执行代码

Executing a code after a promise with nested promises inside it is resolved

javascript

es6-promise

web3