javascript中的for循环内的异步函数调用

Question

Writing a small Instagram like checking bot.

How it works is, i have an object which is a list of users from a chat and their instagram usernames.

So i have this little piece of code here, it iterates over the list, gets the likers of the latest media post of each username and proceeds to check, all while in the loop. However the problem im facing is that there are asynchronous calls inside the loops, and the loop keeps iterating but the results of the async calls come later. However, that is not my desired way of operation. Could someone show me as to how i can overcome this, or the right way to do this in an asynchronous nature? Thanks Below is my code, there is also a comment in there which shows you the format of the list object, just in case anyone is wondering. Thanks

bot.on('/check', (msg) => {
    list['12345'] = {username:'someguy', list:['@the.haider.ali']};
    list['45678'] = {username:'someguy2', list:['@vishnuvayala']};
    if(list.length != 0){
        for(i in list){
            var list2 = JSON.parse(JSON.stringify(list));
            delete list2[i];
            for(x in list2){
                for(y in list2[x].list){
                    let checkis = list2[x].list[y]
                    console.log("Checking "+checkis);
                    getInstaID(checkis).then(function(userid){
                        return getMediaID(userid);
                    }).then(function(mediaid){
                        return getLikers(mediaid);
                    }).then(function(likers){
                        console.log("Last liker is "+likers[0].username);
                    });
                    console.log("Done checking "+checkis);
                }
            }
        }
    }
});

Here's the output i get

Checking @the.haider.ali
Done checking @the.haider.ali
Checking @vishnuvayala
Done checking @vishnuvayala
Last liker is ghetto._boy
Last liker is dk.gayathri

Answer 1

Try with async await. Async function can be blocked by await/promise, there for array iteration can be blocked until await response.

Don't be afraid of Await expressions. It'll just block function till same well known Promise won't be resolved.

Please check if it works.

bot.on('/check', async function(msg){
    list['12345'] = {username:'someguy', list:['@the.haider.ali']};
    list['45678'] = {username:'someguy2', list:['@vishnuvayala']};
    if(list.length != 0){
        for(i in list){
            var list2 = JSON.parse(JSON.stringify(list));
            delete list2[i];
            for(x in list2){
                for(y in list2[x].list){
                    let checkis = list2[x].list[y]
                    console.log("Checking "+checkis);
                    var userid = await getInstaID(checkis);
                    var mediaid = await getMediaID(userid);
                    var likers = await getLikers(mediaid);
                    console.log("Last liker is "+likers[0].username);
                    console.log("Done checking "+checkis);
                }
            }
        }
    }
});

Output should be like

Checking 0
Last liker is likers: 0
Done checking 0
Checking 1
Last liker is likers: 1
Done checking 1
Checking 2
Last liker is likers: 2
Done checking 2