Linked List Kata

linked_list.js

// $ brew install node
// $ npm init
// $ npm install -S mocha chai sinon
//
// $ npm test

var sinon = require("sinon");
var expect = require("chai").expect;

var LinkedList = function() {
  var head, last;

  this.append = function(value) {
    var newNode = { value: value };
    
    if (typeof head === "undefined") {
      head = newNode;
    } else {
      last.next = newNode;
    }

    last = newNode;
  };

  this.each = function(callback) {
    var current = head;

    while (typeof current !== "undefined") {
      callback(current.value);
      current = current.next;
    }
  };
};

describe("LinkedList", function() {
  var list;

  beforeEach(function() {
    list = new LinkedList();
  });

  describe("iterating", function() {
    describe("before appending any elements", function() {
      it("does not call the callback", function() {
        var callback = sinon.spy();

        list.each(callback);
        expect(callback.callCount).to.eql(0);
      });
    });

    describe("after appending one element", function() {
      var element = "A";

      beforeEach(function() {
        list.append(element);
      });

      it("calls the callback once", function() {
        var callback = sinon.spy();

        list.each(callback);
        expect(callback.callCount).to.eql(1);
      });

      it("calls the callback with the element", function() {
        var callback = sinon.spy();

        list.each(callback);
        expect(callback.getCall(0).args).to.eql([element]);
      });
    });

    describe("after appending two elements", function() {
      var first = "A";
      var second = "B";

      beforeEach(function() {
        list.append(first);
        list.append(second);
      });

      it("calls the callback twice", function() {
        var callback = sinon.spy();

        list.each(callback);
        expect(callback.callCount).to.eql(2);
      });

      it("calls the callback with the elements", function() {
        var callback = sinon.spy();

        list.each(callback);
        expect(callback.getCall(0).args).to.eql([first]);
        expect(callback.getCall(1).args).to.eql([second]);
      });
    });

    describe("after appending three elements", function() {
      var first = "A";
      var second = "B";
      var third = "C";

      beforeEach(function() {
        list.append(first);
        list.append(second);
        list.append(third);
      });

      it("calls the callback three times", function() {
        var callback = sinon.spy();

        list.each(callback);
        expect(callback.callCount).to.eql(3);
      });

      it("calls the callback with the elements", function() {
        var callback = sinon.spy();

        list.each(callback);
        expect(callback.getCall(0).args).to.eql([first]);
        expect(callback.getCall(1).args).to.eql([second]);
        expect(callback.getCall(2).args).to.eql([third]);
      });
    });
  });
});