[英]Node js for-loop wait for asynchronous function before next iteration?
I am making a function that refreshes data every so often and I am having issues with the request chain that I have. 我正在创建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。 The problem is that I have a for-loop running the asynchronous requests and the for-loop will finish before the requests are done. 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);
If I were to run this code, it would print: 如果我要运行此代码,它将打印:
0
1
2
3
Success
Success
Success
Success
I know what the issue is. 我知道问题是什么。 It's the fact that the for-loop doesn't wait for the requests to finish. 事实是for循环不等待请求完成。 What I don't know is a work-around for this. 我不知道的是解决这个问题。 Does anyone have any ideas? 有没有人有任何想法?
For completeness, the way to do async things sequentially "by hand" is to use recursion: 为了完整起见,“手动”顺序执行异步事务的方法是使用递归:
function dothings(things, ondone){
function go(i){
if (i >= things.length) {
ondone();
} else {
dothing(things[i], function(result){
return go(i+1);
});
}
}
go(0);
}
You want the async library. 你想要异步库。
For instance, 例如,
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
});
}
Can be written like this instead: 可以这样写:
async.forEachOf(listObj.result, function (result, i, callback) {
varBody.index = i;
varBody.memberID = result.program_member.id;
request(
...
, function () {
// Do more Stuff
// The next iteration WON'T START until callback is called
callback();
});
}, function () {
// We're done looping in this function!
});
There are lots of handy utility functions like this in async that makes working with callbacks much much easier. 在异步中有很多方便的实用程序函数,这使得回调更容易。
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