如何存储 promise 使用的变量？

Question

I am using an API to download some data and I want to store it. I want to make multiple calls using different dates and store all the data together, as well as the date in question, like this:

let rankJson = [];
let rankExport = [];
let ranks = [];

function add_weeks(date, n)  {
    return new Date(date.setDate(date.getDate() + (n * 7)));      
};
for (i = startingDate; i < new Date(); i = add_weeks(i,1)) { 
    // This loops starts at some date I define and adds a week until it reaches a date in the future. 

    let activeYear = i.getFullYear();
    let activeMonth = monthNames[i.getMonth()];
    let activeDay = i.getDate();
    API.function({year: activeYear.toString(), month: activeMonth, day: activeDay.toString()}).then((res) => {

        // This is an API call (its an NPM/Node API) that returns a promise. I then want to store the resulting json array and add the date (i) as new values for each object like so: `

        rankJson = JSON.stringify(res);
        ranks = JSON.parse(rankJson);
        ranks.forEach(function(value){
            rankExport.push({
                "teamName" : value.team.name,
                "teamId": value.team.id,
                "position" : value.place,
                "points" : value.points,
                "posChange" : value.change,
                "rankDay" : activeDay,
                "rankMonth" : i.getMonth() + 1,
                "rankYear" : activeYear,
            })
        });

In essence, I want all of the responses from the API to be stored in one array (don't need it to be in order) with the right date value. Problem is, I don't know how to pass the date variables so that the correct value is applied. When I pass it like this, it seems to be using the last iteration (ie a date in the future). I've also found this to be a bit finicky, mostly because I obviously don't have a lot of experience with promises.

Can anyone help? Thanks

Answer 1

Sounds like you just need to use a closure / IIFE :

(function(i) {
    let activeYear = i.getFullYear();
    let activeMonth = monthNames[i.getMonth()];
    let activeDay = i.getDate();
    API.function({
        year: activeYear.toString(),
        month: activeMonth,
        day: activeDay.toString()
    }).then((res) => {
        // ...
    });
})(i);

The issue right now is that the API call is asynchronous, so by the time you get to the .then , the values of activeYear , activeMonth , activeDay , and i will all have been updated to the last value. By wrapping it in a closure each iteration of the loop will have its own scope.

Answer 2

You could simplify this code by adding all objects to an array and then use Promise.all

var promisses=[]
for (let i = startingDate; i < new Date(); i = add_weeks(i,1)) { 
  promisses.push({year: i.getFullYear().toString(), month: monthNames[i.getMonth()], day: i.getDate().toString()})}
 Promise.all(promisses.map(o=>API.function(o))).then((p) => {
 p.forEach(res=>{
  rankJson=JSON.stringify(res)
  ranks = JSON.parse(rankJson);
    ranks.forEach(function(value){
        rankExport.push({
            "teamName" : value.team.name,
            "teamId": value.team.id,
            "position" : value.place,
            "points" : value.points,
            "posChange" : value.change,
            "rankDay" : activeDay,
            "rankMonth" : i.getMonth() + 1,
            "rankYear" : activeYear,
        })
    });
  })
})