javascript - 运行 3 个 Promise，然后在其他 Promise 完成后运行最后一个 Promise

Question

我正在编写一个 Nodejs Controller 。

我有一整套 promise ，其中每个 promise 都从不同的查询中获取数据

我想启动它们(因为它们需要不同的时间来完成)，一旦它们全部完成，我想启动我的priceCalc函数，它使用收集到的所有数据。

我查看了很多指南和示例，但我不明白 Promise.all 以及它如何在我的案例中发挥作用？

此外，如果其中一个失败，它应该返回错误怎么办？它们必须全部完成，priceCalc 函数才能启动。

(我是 Promise 的新手，所以如果可以的话请让它变得简单:-)))

var findPrice = new Promise(
    (resolve, reject) => {
    priceTable.findOne........

var movePrice = function (data) {
    priceArray = data......

findPrice       
    .then(movePrice)
    .then(fulfilled => console.log('findPrice FINISHED!!!'))
    .catch(error => console.log(error.message));        


var findhotdeal = new Promise(
    (resolve, reject) => {
    hotdealTable.aggregate.........

var movehotdeal = function (data) {
    hotdealArray = data;.......     

findhotdeal       
    .then(movehotdeal)
    .then(fulfilled => console.log('findhotdeal FINISHED!!!'))
    .catch(error => console.log(error.message));


var calculatePrice = function () {
    // Use the data from the previous promises once they all finished

}

Answer 1

如果您需要所有 4 个 Promise 的解析值

var findPrice = new Promise(
    (resolve, reject) => {
    priceTable.findOne........

var movePrice = function (data) {
    priceArray = data......

var findhotdeal = new Promise(
    (resolve, reject) => {
    hotdealTable.aggregate.........

var movehotdeal = function (data) {
    hotdealArray = data;.......     

var calculatePrice = function ([fp, mp, fh, mh]) {
    // fp == resolved value of findPrice
    // mp == resolved value of movePrice
    // fh == resolved value of findhotdeal
    // mh == resolved value of movehotdeal
}

Promise.all([findPrice, findPrice.then(movePrice), findhotdeal, findhotdeal.then(movehotdeal)])
    .then(calculatePrice)
    .catch(err => { /* handle errors here */})

注意:

var calculatePrice = function ([fp, mp, fh, mh]) {
    // fp == resolved value of findPrice
    // mp == resolved value of movePrice
    // fh == resolved value of findhotdeal
    // mh == resolved value of movehotdeal
}

是 ES2015+ 的简写

var calculatePrice = function (r) {
    var fp = r[0],
        mp = r[1],
        fh = r[2],
        mh = r[3];

    // fp == resolved value of findPrice
    // mp == resolved value of movePrice
    // fh == resolved value of findhotdeal
    // mh == resolved value of movehotdeal
}

Given that movePrice and movehotdeal are not asyncrhonous

var findPrice = new Promise((resolve, reject) => {
    priceTable.findOne........
});

var findhotdeal = new Promise((resolve, reject) => {
    hotdealTable.aggregate.........
});

var calculatePrice = function ([fp, fh]) {
    priceArray = fp;
    hotdealArray = fh;
    // fp == resolved value of findPrice
    // fh == resolved value of findhotdeal
}

Promise.all([findPrice, findhotdeal])
    .then(calculatePrice)
    .catch(err => { /* handle errors here */})