how for loop work in node.js?

Question

In my loop i have a group id like this

  ****variable i value****
      groupid  0 199
      groupid  1 200
      groupid  2 201

but in for loop its always take group 201 in first iteration why this happend. here is my code.

for (var i = 0; i < groupdata.length; i++) {
    console.log('groupid', i, groupdata[i].id);
    var groupname = groupdata[i].name;
    var groupid = groupdata[i].id;
    var groupType = groupdata[i].groupType;
    var getuserdata = {
        "groupID": groupdata[i].id,
        "groupType": groupdata[i].groupType,
        "token": req.usersession.token
    };
    var digest = BASE.utils.hmac("sha1", "A12AA418-1F28-4464-8B67-29CBD02BC45C-F048B14F-F3E3-4F97-A522-F2275A364A0E", JSON.stringify(getuserdata));

    var postData = {
        "groupID": groupdata[i].id,
        "groupType": groupdata[i].groupType,
        "digest": digest,
        "token": req.usersession.token
    };



    var groupUserData = BASE.utils.base64encode(BASE.utils.base64encode(JSON.stringify(postData)));


    BASE.request({
            url: "http://example.com/getGroupUsers/",
            method: "POST",
            headers: {

                "content-type": "application/json",
            },
            body: groupUserData
        },
        function(err, result, groupUserdata) {

            var groupuserdata = JSON.parse(groupUserdata);
            console.log('first groupusers.....', i, groupuserdata);

            var groupids = groupuserdata.groupUsers.filter(function(group) {
                if (group.userID != contactid) {
                    userbody.groups.map(function(usr) {
                        if (usr.id == groupid) {
                            console.log('maingroupid....', usr.id);
                            console.log('current loop groupid..', groupid);
                            group.groupData = usr;
                        }
                        return usr;
                    })
                    return group;
                }
            });
            //console.log(groupids);
            newgroupdta.push(groupids);
            //res.send(groupids);
            //  console.log(groupids);
            //console.log('.............',newgroupdta);
        });
}
            /* end for loop */

        }); 

groupdata have below values

groupdata.... [ { groupType: '1',
    id: '199',
    unreadMessages: '0',
    ownerId: '339',
    name: 'xyz' },   { groupType: '1',
    id: '200',
    unreadMessages: '0',
    ownerId: '339',
    name: 'second group' },   { groupType: '1',
    id: '201',
    unreadMessages: '0',
    ownerId: '339',
    name: 'new one' } ]

groupusers data is like below

 { groupUsers: [ { userID: '0' }, { userID: '31' }, { userID: '326' } ] }

Basically i want to check contactid which is 326 exist in groupusers if no then return that particular groupdata in array like {groupdata:[{groupname:,groupid:}]}

/*********************edit***********************/
var count = 0;
                    var i =0;
                function outer(data){

                         if(count==groupdata.length)break;

                        var groupname = groupdata[i].name;
                        var groupid = groupdata[i].id;
                        var groupType =groupdata[i].groupType;
                    var getuserdata = {
                        "groupID" :groupdata[i].id,
                         "groupType" : groupdata[i].groupType,
                         "token":req.usersession.token   


                    };



                var digest = BASE.utils.hmac("sha1", "A12AA418-1F28-4464-8B67-29CBD02BC45C-F048B14F-F3E3-4F97-A522-F2275A364A0E", JSON.stringify(getuserdata));

                var postData = {
                "groupID" :groupdata[i].id,
                "groupType" : groupdata[i].groupType,
                "digest"      :  digest,
                "token" : req.usersession.token           
                };      

                var groupUserData = BASE.utils.base64encode(BASE.utils.base64encode(JSON.stringify(postData)));


                BASE.request({
                url : "http://201.206.158.254:8080/BACKSTAFF/service/getGroupUsers/",
                method :"POST",
                headers : {

                    "content-type": "application/json",
                },
                    body :groupUserData
                },
            function (err,result,groupUserdata) {

                    console.log(groupUserdata); 

                    });
                    i++;
                    outer(groupdata[count++]);
                    }
/***************end edit *************************/

Answer 1

You have written asynchronous callback function inside for loop . As per your code above BASE.request({},function(){}) method will be called asynchronously , it will not wait for result and for loop will move to next .

There are multiple ways to handle this :

1) Async.js

2) Recursion ( Remove for and call next method from inside callback and at last break and come out of loop)

var count = 0;
function outer(data){
   BASE.request({},function(){
        if(count==groupdata.length)return;
        //whatever logic        
        outer(groupdata[count++]);
   })
}

3) Eventemitter can also be used