Question

我正在制作一个每隔一段时间刷新一次数据的函数，而且我遇到了我的请求链问题。问题是我有一个for循环运行异步请求，for循环将在请求完成之前完成。

setInterval(function(){ // this updates the total hours of all members every 10 seconds
    request({ // this gets all of the loyalty program members
        url: "",//omitted
        method: "GET"
    },
        function(listError, listResponse, listBody) {
            if(listError == null && listResponse.statusCode == 200) {
                var varBody = {};
                var listObj = JSON.parse(listBody);
                for(var i = 0; i < listObj.result.length; i++) { // parses through all of the members to update their hours

                    console.log(i);//****PRINT STATEMENT

                    varBody.index = i;
                    varBody.memberID = listObj.result[i].program_member.id;
                    request({ //we do this request to get the steam ID of the program member
                            url: "",//omitted
                            method: "GET"
                        },
                        function(fanError, fanResponse, fanBody) {

                            var fan = JSON.parse(fanBody);
                            if(fanError == null && fanResponse.statusCode == 200 && fan.result.profiles.length != 0) { // make sure that the profile isn't empty
                                request({
                                        url:"",//omitted
                                        method: "GET"
                                    },
                                    function(hourError, hourResponse, hourBody) {
                                        if (hourError == null && hourResponse.statusCode == 200) {
                                            var gameList = JSON.parse(hourBody);
                                            var minutes = 0;
                                            for (var j = 0; j < gameList.response.games.length; j++) { // for loop to calculate the minutes each user has on steam
                                                minutes += gameList.response.games[j].playtime_forever;
                                            }
                                            var deltaHours = 1;
                                            if(deltaHours != 0) {
                                                var transaction = { // updated member object to be inserted
                                                    pointsearned: deltaHours,
                                                    pointsused: 0,
                                                    loyaltyprogram_id: loyaltyID,
                                                    programmember_id: memberID
                                                };
                                                request({ // POST request to update the member
                                                        url: "",//omitted
                                                        method: "POST",
                                                        body: JSON.stringify(transaction),
                                                        headers: {
                                                            "Content-Type": "application/json"
                                                        }
                                                    },
                                                    function(updateError, updateRes, updateBody) {
                                                        if(updateError == null && updateRes.statusCode == 200) {
                                                            console.log("Success");//****PRINT STATEMENT
                                                        }
                                                    }
                                                );
                                            }
                                        }
                                    }
                                );
                            }
                        }
                    );
                }
            }
            console.log("Users Updated"); //****PRINT STATEMENT
        }
    );
}, 10000);

如果我要运行此代码，则会打印：

0
1
2
3
Success
Success
Success
Success

我知道问题是什么。事实上，for-loop并没有等待请求完成。我不知道的是解决这个问题的方法。有没有人有任何想法？

Answer 1

为了完整性，顺序执行异步事务的方式＆＃34;手工＆＃34;是使用递归：

function dothings(things, ondone){
    function go(i){
        if (i >= things.length) {
            ondone();
        } else {
            dothing(things[i], function(result){
                return go(i+1);
            });
        }
    }
    go(0);
}

Answer 2

您需要async库。

例如，

library(dplyr)
library(ggmap)
library(rgdal)
library(broom)

# Read in shapefile, project into long-lat
# Create 'tbox' which is a minimum bounding box around the shapefile

tracts <- readOGR(dsn = ".", layer = "CensusTracts2010") %>%
  spTransform("+proj=longlat +ellps=WGS84")
tbox <- bbox(tracts)

# Plot data
tract_plot <- tidy(tracts)

DetroitMap <- qmap("Detroit", zoom = 11)

DetroitMap + geom_polygon(data = tract_plot, aes(x = long, y = lat, group = id), color = "black", fill = NA) +
  coord_cartesian(xlim = c(tbox[1,1], tbox[1,2]),
                  ylim = c(tbox[2,1], tbox[2,2]))

可以这样写：

for(var i = 0; i < listObj.result.length; i++) {
    varBody.index = i;
    varBody.memberID = listObj.result[i].program_member.id;
    request(
        ...
    , function () {
        // Do more Stuff
    });
}

在异步中有很多方便的实用程序函数，这使得回调变得更加容易。

节点js for-loop在下一次迭代之前等待异步函数？

2 个答案: