tooManyItreration.js

const _ = require('lodash');

const input = [{
    "ActiveMembers": [{
        "Id": 101,
        "Name": "alpha"
    }, {
        "Id": 102,
        "Name": "bravo"
    }],
    "Contents": [{
        "Id": 2001,
        "RowId": "517",
        "Time": "19 Jan 2017",
        "ViewCount": 1124
    }, {
        "Id": 2002,
        "RowId": "518",
        "Time": "Today, 07:02 PM",
        "ViewCount": 62
    }],
    "TotalUsers": 3,
    "UsersDetails": "2 members, 1 anonymous users"
}, {
    "ActiveMembers": [{
        "Id": 101,
        "Name": "alpha"
    }, {
        "Id": 103,
        "Name": "charlie"
    }, {
        "Id": 104,
        "Name": "delta"
    }, {
        "Id": 105,
        "Name": "bravo"
    }],
    "Contents": [{
        "Id": 2002,
        "RowId": "519",
        "Time": "27 Jun 2017",
        "ViewCount": 4833
    }, {
        "Id": 2041,
        "RowId": "525",
        "Time": "17 Feb 2015",
        "ViewCount": 24491
    }],
    "TotalUsers": 23,
    "UsersDetails": "4 members, 19 anonymous users"
}];

/*
var contents = Array.prototype.concat.apply([], input.map(i => i.Contents));
var activeMembers = _.uniqBy(Array.prototype.concat.apply([], input.map(i => i.ActiveMembers)), (i) => i.Id);
var totalUsers = number = _.sumBy(input, (i) => i.TotalUsers);
var userDetails = string = input.map(i => i.UsersDetails).join(' ; ');

const result = new Object();
result.Contents = contents;
result.ActiveMembers = activeMembers;
result.TotalUsers = totalUsers;
result.UserDetails = userDetails;

console.log(JSON.stringify(result));
*/

var contents = [];
var activeMembers = [];
var totalUsers = 0;
var usersDetails = "";

input.forEach(function (element) {

    element.ActiveMembers.forEach(function (activeMember) {
        const recordExist =  activeMembers.some(am=>am.Id===activeMember.Id);
        if (!recordExist) { activeMembers.push(activeMember); }
    });

    contents = contents.concat(element.Contents);
    totalUsers += element.TotalUsers;
    usersDetails += element.UsersDetails + ";"
});


const result = new Object();
result.Contents = contents;
result.ActiveMembers = activeMembers;
result.TotalUsers = totalUsers;
result.UserDetails = usersDetails.slice(0, -1);

console.log(JSON.stringify(result));