A JavaScript Calculator with Closure

JavaScript Calculator with Closure

/*
function Calculator() {
  this.add = function(input) {
    var result = 0;
    for(i = 0; i<input.length; ++i) {
      result += input[i];
    }
    return result;
  }

  this.multiply = function(input) {
    var result = 1;
    for(i=0; i<input.length; ++i) {
      result *= input[i];
    }
    return result;
  }
}
*/

function Calculator() {
  var operator = function(result, input) { return result + input; };
  this.add = function(input){
    return operation(input, operator);
  };

  this.multiply = function(input){
    return operation(input, function(result, input) { return result * input; });
  }

  this.subtract = function(input){
    return operation(input, function(result, input) { return result - input; });
  }
  
  this.divide = function(input){
    return operation(input, function(result, input) { return result / input; });
  }

  function operation(input, operator) {
    var result = input.shift();
    for(i = 0; i < input.length; i++){
      result = operator(result, input[i]);
    }
    return result;
  }
}

describe("Calculator", function() {
  var calculator;
  beforeEach(function() {
    calculator = new Calculator();
  });

  describe("Arithmetic operations on an array input", function() {
    it("creates a new Calculator object", function() {
      expect(calculator).not.toBeNull();
     });

    it("adds two numbers together", function() {
      expect(calculator.add([1,0])).toEqual(1);
    });

    it("adds three numbers together", function() {
      expect(calculator.add([1,2,3])).toEqual(6);
    });

    it("multiplies two numbers", function(){
      expect(calculator.multiply([1,2])).toEqual(2);
    });

    it("returns the difference between the numbers passed in", function(){
      expect(calculator.subtract([3,2])).toEqual(1);
    });

    it("returns the quotient of the numbers passed in", function(){
      expect(calculator.divide([10,2,5])).toEqual(1);
    });
  });
});