Tell us what’s happening:

Instruction says:
Run the code in the editor. It’s using a method that has side effects in the program, causing incorrect output. The final list of open tabs should be [‘FB’, ‘Gitter’, ‘Reddit’, ‘Twitter’, ‘Medium’, ‘Netflix’, ‘YouTube’, ‘Vine’, ‘GMail’, ‘Work mail’, ‘Docs’, ‘freeCodeCamp’, ‘new tab’] but the output will be slightly different.

Work through the code and see if you can figure out the problem, then advance to the next challenge to learn more.

But actually right output should be [ ‘FB’, ‘Gitter’, ‘Reddit’, ‘Twitter’, ‘Medium’, ‘new tab’, ‘Netflix’, ‘YouTube’, ‘Vine’, ‘GMail’, ‘Work mail’, ‘Docs’, ‘freeCodeCamp’, ‘new tab’ ]

You’ve missed one new tab (that was opened for cat memes), I guess.

Your code so far

// tabs is an array of titles of each site open within the window
var Window = function(tabs) {
  this.tabs = tabs; // we keep a record of the array inside the object

// When you join two windows into one window
Window.prototype.join = function (otherWindow) {
  this.tabs = this.tabs.concat(otherWindow.tabs);
  return this;

// When you open a new tab at the end
Window.prototype.tabOpen = function (tab) {
  this.tabs.push('new tab'); // let's open a new tab for now
  return this;

// When you close a tab
Window.prototype.tabClose = function (index) {
  var tabsBeforeIndex = this.tabs.slice(0, index); // get the tabs before the tab
  var tabsAfterIndex = this.tabs.slice(index + 1); // get the tabs after the tab

  this.tabs = tabsBeforeIndex.concat(tabsAfterIndex); // join them together 
  return this;

// Let's create three browser windows
var workWindow = new Window(['GMail', 'Inbox', 'Work mail', 'Docs', 'freeCodeCamp']); // Your mailbox, drive, and other work sites
var socialWindow = new Window(['FB', 'Gitter', 'Reddit', 'Twitter', 'Medium']); // Social sites
var videoWindow = new Window(['Netflix', 'YouTube', 'Vimeo', 'Vine']); //  Entertainment sites

// Now perform the tab opening, closing, and other operations
var finalTabs = socialWindow
                    .tabOpen() // Open a new tab for cat memes
                    .join(videoWindow.tabClose(2)) // Close third tab in video window, and join


Your browser information:

User Agent is: Mozilla/5.0 (X11; Ubuntu; Linux i686; rv:59.0) Gecko/20100101 Firefox/59.0.

Link to the challenge:


If you think there is an error in a challenge, please create a detailed GitHub Issue describing it.


I’m so sorry, but I’m a newbie in coding. So I don’t even know how to work with GitHub (have no experience). But I’ll try, thanks =)


You should see that the current Output is slightly different. You should see what happen to the object videoWindow after it runs tabsBeforeIndex (0,2)…