creating curry functions to master functional programming. In Progress...

execute.js

var products = [
    {
        id: 1,
        name: 'IPhone X',
        price: 900
    },
    {
        id: 2,
        name: 'Samsung S8',
        price: 700
    },
    {
        id: 3,
        name: 'Moto X',
        price: 300
    },
    {
        id: 4,
        name: 'Nokia N6',
        price: 200
    }
]

// Curry function that return value of a property in an object
function prop(property) {
    return function (arr) {
        return arr.reduce(function (acc, item) {
            acc.push(item[property]);
            return acc;
        }, []);
    }
}

// Curry function that apply map on a given array
function map(fn) {
    return function () {
        return fn();
    }
}

// Curry function that apply filter on given array
function filter(fn) {

}

// Function that will convert provied string to upper case
function toUpper(str) {
    return function () {
        return str.toUpperCase();
    }
}

// Curry function that will identify whether the number passed to 
// second function in curry is less than first number passed in curry
function lessThan(num1) {
    return function (arr) {
        return arr.filter(function (item) {
            return item.price < num1;
        });
    }; 
}

// This function will expect multiple arguments as functions.
// It will execute them from right-to-left and will pass the 
// return value of a function to next function in the chain
// Hint: Don't convert arguments to array!
function compose(fn) {
    return function (arr) {
        // Some magic has to be done here.
    }
}

var getUpperProductNames = compose(map(toUpper), map(prop('name')));
var productsCheapProducts = compose(filter(compose(lessThan(400), prop('price'))));

console.log(getUpperProductNames(products)); // ["IPHONE X", "SAMSUNG S8", "MOTO X", "NOKIA N6"]

console.log(productsCheapProducts(products));
  // [{
  //      "id": 3,
  //      "name": "Moto X",
  //      "price": 300
  //  },
  //  {
  //      "id": 4,
  //      "name": "Nokia N6",
  //      "price": 200
  // }]