7. Advanced JavaScript

Activity 8: Creating a User Tracker

Solution

1. Open the Activity08.js file and define logUser. It will add the user to the userList argument. Make sure no duplicates are added:

   function logUser(userList, user) {
   if(!userList.includes(user)) {
   userList.push(user);
   }
   }

   Here, we used an includes method to check whether the user already exists. If they don't, they will be added to our list.

2. Define userLeft. It will remove the user from the userList argument. If the user doesn't exist, it will do nothing:

   function userLeft(userList, user) {
   const userIndex = userList.indexOf(user);
   if (userIndex >= 0) {
       userList.splice(userIndex, 1);
   }
   }

   Here, we are using indexOf to get the current index of the user we want to remove. If the item doesn't exist, indexOf will return –1, so we are only using splice to remove the item if it exists.

3. Define numUsers, which returns the number of users currently inside the list...