JS - 承诺以错误的顺序执行

Question

我的代码试图做的是创建一个具有一些动态属性的对象数组，这些属性将作为某些函数的结果被填充。我正在尝试使用承诺，否则我的模板会在函数完成之前呈现，并且这些对象的属性将为 null 或未定义，从而导致模板出错。

这是第一个函数

fetchUserPortfolioCoins({ commit, dispatch, state, rootGetters }) {
        const promises = []
        promises.push(dispatch('utilities/setLoading', true, { root: true })) // start loader
        if (!rootGetters['auth/isAuthenticated']) {
            // if user isn't logged, pass whatever is in the store, so apiDetails will be added to each coin
            let coins = state.userPortfolioCoins
            coins.forEach(coin => { promises.push(dispatch('createAcqCostConverted', coin)) })
            commit('SET_USER_COINS', { coins, list: 'userPortfolioCoins' })
        } else {
            // otherwise, pass the response from a call to the DB coins
            Vue.axios.get('/api/coins/').then(response => {
                let coins = response.data
                coins.forEach(coin => { promises.push(dispatch('createAcqCostConverted', coin)) })
                commit('SET_USER_COINS', { coins, list: 'userPortfolioCoins' })
            })
        }
        Promise.all(promises)
            .then(() => {
                commit('SET_USER_PORTFOLIO_OVERVIEW')
                dispatch('utilities/setLoading', false, { root: true })
            })
            .catch(err => { console.log(err) })
    },

调用这个的：

createAcqCostConverted({ dispatch, rootState }, coin) {
    const promises = []
    // this check is only going to happen for sold coins, we are adding sell_price_converted in case user sold in BTC or ETH
    if (coin.sell_currency === 'BTC' || coin.sell_currency === 'ETH') {
        const URL = `https://min-api.cryptocompare.com/data/pricehistorical?fsym=${coin.coin_symbol}&tsyms=${rootState.fiatCurrencies.selectedFiatCurrencyCode}&ts=${coin.sold_on_ts}`
        promises.push(Vue.axios.get(URL, {
            transformRequest: [(data, headers) => {
                delete headers.common.Authorization
                return data
            }]
        }))
    }
    // if user bought with BTC or ETH we convert the acquisition cost to the currently select fiat currency, using the timestamp
    if (coin.buy_currency === 'BTC' || coin.buy_currency === 'ETH') {
        const URL = `https://min-api.cryptocompare.com/data/pricehistorical?fsym=${coin.coin_symbol}&tsyms=${rootState.fiatCurrencies.selectedFiatCurrencyCode}&ts=${coin.bought_on_ts}`
        promises.push(Vue.axios.get(URL, {
            transformRequest: [(data, headers) => {
                delete headers.common.Authorization
                return data
            }]
        }))
    } else {
        // if the selected fiatCurrency is the same as the buy_currency we skip the conversion
        if (coin.buy_currency === rootState.fiatCurrencies.selectedFiatCurrencyCode) {
            coin.acquisition_cost_converted = NaN
            return coin
            // otherwise we create the acq cost converted property
        } else promises.push(dispatch('fiatCurrencies/convertToFiatCurrency', coin, { root: true }))
    }
    Promise.all(promises)
        .then(response => {
            const value = response[0].data[coin.coin_symbol][rootState.fiatCurrencies.selectedFiatCurrencyCode]
            if (coin.sell_currency === 'BTC' || coin.sell_currency === 'ETH') coin.acquisition_cost_converted = value
            if (coin.buy_currency === 'BTC' || coin.buy_currency === 'ETH') coin.acquisition_cost_converted = value
            return coin
        })
        .catch(err => { console.log(err) })
},

问题是第一个函数没有等待第二个函数完成。我该如何调整此代码来解决问题？

谢谢

Answer 1

您正在同时执行所有承诺。 Promise.all 不按顺序执行。您传递给它的数组的顺序无关紧要。无论顺序如何，它都会在它们全部完成时简单地解决。

执行发生在您调用函数时，甚至在您将它们推入数组之前。

如果您需要等待第一个完成后再调用第二个。您需要在第一个 .then 函数中调用第二个。例如...

dispatch('utilities/setLoading', true, { root: true }).then(resultOfSetLoading => {
   return Promise.all(coins.map(coin =>  dispatch('createAcqCostConverted', coin)))
}).then(resultOfCreateQcqCostConverted => {
   // all createAcqCostConverted are complete now
})

所以现在，dispatch('utilities/setLoading') 将首先运行。然后，一旦完成，dispatch('createAcqCostConverted') 将为每个硬币运行一次（同时因为我使用 Promise.all）。

我建议您阅读更多有关 Promise.all 工作原理的内容。很自然地认为它会按顺序解决它们，但事实并非如此。

Answer 2

在我阅读了你们中的一些人的回复后，这就是我设法使其工作的方式（对于注销用户和登录用户，2 种不同的方法），不确定它是否是最干净的方法。

第一个函数：

fetchUserPortfolioCoins({ commit, dispatch, state, rootGetters }) {
    const setCoinsPromise = []
    let coinsToConvert = null
    // start loader in template
    dispatch('utilities/setLoading', true, { root: true })
    // if user is logged off, use the coins in the state as dispatch param for createAcqCostConverted
    if (!rootGetters['auth/isAuthenticated']) setCoinsPromise.push(coinsToConvert = state.userPortfolioCoins)
    // otherwise we pass the coins in the DB
    else setCoinsPromise.push(Vue.axios.get('/api/coins/').then(response => { coinsToConvert = response.data }))

    // once the call to the db to fetch the coins has finished
    Promise.all(setCoinsPromise)
        // for each coin retrived, create the converted acq cost
        .then(() => Promise.all(coinsToConvert.map(coin => dispatch('createAcqCostConverted', coin))))
        .then(convertedCoins => {
            // finally, set the portfolio coins and portfolio overview values, and stop loader
            commit('SET_USER_COINS', { coins: convertedCoins, list: 'userPortfolioCoins' })
            commit('SET_USER_PORTFOLIO_OVERVIEW')
            dispatch('utilities/setLoading', false, { root: true })
        }).catch(err => { console.log(err) })
},

createAcqCostConverted 函数：

createAcqCostConverted({ dispatch, rootState }, coin) {
    const promises = []
    // this check is only going to happen for sold coins, we are adding sell_price_converted in case user sold in BTC or ETH
    if (coin.sell_currency === 'BTC' || coin.sell_currency === 'ETH') {
        const URL = `https://min-api.cryptocompare.com/data/pricehistorical?fsym=${coin.coin_symbol}&tsyms=${rootState.fiatCurrencies.selectedFiatCurrencyCode}&ts=${coin.sold_on_ts}`
        promises.push(Vue.axios.get(URL, {
            transformRequest: [(data, headers) => {
                delete headers.common.Authorization
                return data
            }]
        }))
    }
    // if user bought with BTC or ETH we convert the acquisition cost to the currently select fiat currency, using the timestamp
    if (coin.buy_currency === 'BTC' || coin.buy_currency === 'ETH') {
        const URL = `https://min-api.cryptocompare.com/data/pricehistorical?fsym=${coin.coin_symbol}&tsyms=${rootState.fiatCurrencies.selectedFiatCurrencyCode}&ts=${coin.bought_on_ts}`
        promises.push(Vue.axios.get(URL, {
            transformRequest: [(data, headers) => {
                delete headers.common.Authorization
                return data
            }]
        }))
    } else {
        // if the selected fiatCurrency is the same as the buy_currency we skip the conversion
        if (coin.buy_currency === rootState.fiatCurrencies.selectedFiatCurrencyCode) {
            promises.push(coin.acquisition_cost_converted = NaN)
            // otherwise we create the acq cost converted property
        } else promises.push(dispatch('fiatCurrencies/convertToFiatCurrency', coin, { root: true }))
    }
    return Promise.all(promises)
        .then(response => {
            if (coin.sell_currency === 'BTC' || coin.sell_currency === 'ETH') {
                const value = response[0].data[coin.coin_symbol][rootState.fiatCurrencies.selectedFiatCurrencyCode]
                coin.acquisition_cost_converted = value
            }
            if (coin.buy_currency === 'BTC' || coin.buy_currency === 'ETH') {
                const value = response[0].data[coin.coin_symbol][rootState.fiatCurrencies.selectedFiatCurrencyCode]
                coin.acquisition_cost_converted = value
            }
            return coin
        })
        .catch(err => { console.log(err) })
},

在第二个函数中我不需要做太多调整，我只是为 Promise.all 添加了一个 "return" 并更正了 if/else 以仅在特定原因中使用响应，因为从响应生成的 "value" 变量仅在这两种情况下有效，在其他情况下我可以简单地 return "coin".

希望它有意义，如果需要，可以在这里更好地解释任何事情and/or讨论如何使这段代码更好（我觉得它不是，但不确定为什么 :P ）

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