What's wrong with "Window.prototype.tabClose' method?

Anybody know what’s wrong with “Window.prototype.tabClose” method?

Question:
Examine the code in the editor. It’s using a method that has side effects in the program, causing incorrect behaviour. The final list of open tabs, stored in finalTabs.tabs , should be ['FB', 'Gitter', 'Reddit', 'Twitter', 'Medium', 'new tab', 'Netflix', 'YouTube', 'Vine', 'GMail', 'Work mail', 'Docs', 'freeCodeCamp', 'new tab'] but the list produced by the code is slightly different.

Change Window.prototype.tabClose so that it removes the correct tab.

   **Your code so far**

// tabs is an array of titles of each site open within the window
const 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) {

 // Only change code below this line

 const tabsBeforeIndex = this.tabs.splice(0, index); // Get the tabs before the tab
 const tabsAfterIndex = this.tabs.splice(index + 1); // Get the tabs after the tab

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

 // Only change code above this line

 return this;
};

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

// Now perform the tab opening, closing, and other operations
const finalTabs = socialWindow
 .tabOpen() // Open a new tab for cat memes
 .join(videoWindow.tabClose(2)) // Close third tab in video window, and join
 .join(workWindow.tabClose(1).tabOpen());
console.log(finalTabs.tabs);
   **Your browser information:**

User Agent is: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/100.0.4896.88 Safari/537.36

Challenge: Understand the Hazards of Using Imperative Code

Link to the challenge: