Underscore.js

 //# usable is web, mobile, server
 //# don't change native prototypes

        function Person(name, lname, age) {
            this.name = name;
            this.lname = lname;
            this.age = age;
        }

        var people = [
            new Person("jonh", "smith", 15),
            new Person("miss", "world", 2),
            new Person("ace", "base", 1)
        ];

        /// foreach (if no native forEach)
        // gives item value, index, all collection
        var numbers = [1, 2, 3, 4, 5, 6];
        _.each(numbers, function (item, index, collection) { console.log("%s %s %s", item, index, collection); });
        /// map (if no native map)
        var numbers = [0, 2, 3, 1, 3, 2];
        var numbersNames = ['zero','one', 'two', 'three'];
        var numbersWithNames = _.map(numbers, function (n) { return numbersNames[n]; });
        console.log(numbersWithNames);
        /// filter
        var numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
        function isEven(num) { return num % 2 }
        var odd = _.filter(numbers, isEven);
        var even = _.reject(numbers, isEven);
        var result = _.filter(people, function(p){ return p.lName == "s" }) //people with last name starts with "P" (true or false -> filter)

        /// where
        //var filteredPeople = _.filter(people, /*{age : 13 }*/ { age: 13, name: "pesho" }); //all people who have age and name (no OR) only AND

        ///all/every && some/any -> does all or atleast one elements in collection met certain condition

        ///pluck -> return only 1 prop value of collection
        // var people = [.....] _.pluck(people, "lname"); // _.map(people, function(p){return p.lname});

        ///sort by && group by
        var sortedPeople = _.sortBy(people, "fname");
        var groups = _.groupBy(people, "name");
        console.log(groups);

        //########## arrays #########//

        ///_.first() && _.initial() _.first(people) or _.first(people, 2) .... initial all without last n

        /// _.last() && _.rest() -> select last n elements

        /// _.compact() -> remove all false values

        /// _.union() && _.intersect

        /// _.memoize(function(params)) -> cash function result for this params

        /// _.compose(third, second, first) -> third(second(first())) -> pass return param to next function


        //######### objects ##########//

        /// keys(obj)

        /// invert(obj) props <--> values

        /// extend(obj, props) -> prototypal inheritance

        //######

        _.chain(people).sortBy('fname').plunk('lname') ........ // several operations on this collection