Group Persons

/* Write a JavaScript function group(persons) that groups an array of persons by age, first or last name.
 Create a Person constructor to add every person in the person array. The group(persons) function must return
 an associative array, with keys – the groups (age, firstName and lastName) and values – arrays with persons
 in this group. Print on the console every entry of the returned associative array. */

"use strict";

function Person(firstName, lastName, age) {
    return {
        "firstName": firstName,
        "lastName": lastName,
        "age": age,
        "toString": function () {
            return this.firstName + ' ' + this.lastName + '(age ' + this.age + ')';
        }
    };
}

function group(persons) {
    var keyGroup = arguments[1];
    if (!keyGroup) return persons;

    var groupObj = {};
    for (var i = 0; i < persons.length; i += 1) {
        var person = persons[i];
        var groupName = 'Group ';
        switch (keyGroup) {
            case 'firstName':
                groupName = groupName.concat(person.firstName);
                break;
            case 'lastName':
                groupName = groupName.concat(person.lastName);
                break;
            case 'age':
                groupName = groupName.concat(person.age);
                break;
        }

        if (!(groupName in groupObj)) {
            groupObj[groupName] = [];
        }

        groupObj[groupName].push(person.toString());
    }

    return groupObj;
}


var people = [];
people.push(new Person("Scott", "Guthrie", 38));
people.push(new Person("Scott", "Johns", 36));
people.push(new Person("Scott", "Hanselman", 39));
people.push(new Person("Jesse", "Liberty", 57));
people.push(new Person("Jon", "Skeet", 38));

console.log(group(people, 'firstName'));
console.log(group(people, 'age'));
console.log(group(people, 'lastName'));