Awesome Calculator

calculator.js

function Calculator() {}

function reduceArgs(operation) {
    return function() {
        var args = Array.prototype.slice.call(arguments);
        var ops = {
            '+': function(x, y) {
                return x + y;
            },
            '-': function(x, y) {
                return x - y;
            },
            '/': function(x, y) {
                return x / y;
            },
            '*': function(x, y) {
                return x * y;
            }
        };
        var result = args.reduce(function(prev, curr) {
            return ops[operation](prev, curr);
        }, 0);
        return result;
    };
}
Calculator.prototype.add = reduceArgs('+');
Calculator.prototype.subtract = reduceArgs('-');
Calculator.prototype.multiply = reduceArgs('*');
Calculator.prototype.divide = reduceArgs('/');
module.exports = Calculator;


var Calculator = require('../../app/scripts/calculator.js');
var expect = require('chai').expect;
var context = describe;
//MOCHA + CHAI


describe('Calculator App: ', function(){
 var calc;

 context('Interface: ', function(){
   before(function(){
     calc = new Calculator();
   });
   it('Should exist', function(){
     expect(Calculator).to.be.an('function');
   });
   it('Should be a constructor function', function(){
     expect(calc).to.be.an.instanceof(Calculator);
   });
   it('should have a add method', function(){
    expect(calc).to.respondTo('add'); 
   });
   it('should have a subtract method', function(){
    expect(calc).to.respondTo('subtract'); 
   });
   it('should have a multiply method', function(){
    expect(calc).to.respondTo('multiply'); 
   });
   it('should have a divide method', function(){
    expect(calc).to.respondTo('divide'); 
   });
 });
 context("Implementation of Calculator: ",function() {
   before(function(){
     calc = new Calculator();
   });
   it('should add two numbers', function(){
     expect(calc.add(1,3)).to.equal(4);
   });  
   it('should also sum an array of numbers ',function() {
     expect(calc.add(1,2,3,4,5)).to.equal(15);
   });
 });

});

ops[operation](prev, curr);

and

var ops = {
            '+': function(x, y) {
                return x + y;
            },
            '-': function(x, y) {
                return x - y;
            },
            '/': function(x, y) {
                return x / y;
            },
            '*': function(x, y) {
                return x * y;
            }
        };

Can you explain the structure of the code above help me?