DE | The Elevator

Learning Goals

After this learning unit, you will be able to:

• Build your own elevator using node asynchrony concepts
• Create as many elevator requests as you want and save them in a queue
• Create callback functions to respond asynchronously to the orders received
• Original idea: http://play.elevatorsaga.com/

Introduction

Elevators are a common device in real-life that requires asynchrony. In this Lab, we are going to create an elevator able to respond to different asynchronous requests.

The elevator will have a queue where it's going to store all the requests in the order they are made. Then, the elevator will move up or down depending on the next floor requested. Once it arrives to the actual requested floor, it will go the next one until there are no more requests in the queue.

Requirements

• Fork this repo
• Clone this repo into your ~/code/labs

Submission

Upon completion, run the following commands

$ git add .
$ git commit -m "done"
$ git push origin master

Navigate to your repo and create a Pull Request -from your master branch to the original repository master branch.

In the Pull request name, add your name and last names separated by a dash "-"

Deliverables

In your starter code folder you will find every file you need to finish the game. Push every file needed to make your game work properly.

Exercise

Iteration 1

In the starter_code we have three files:

1. elevator.js

• For the logic of the elevator: accepting requests, moving up or down, etc.

1. person.js

• For a person class with a name, the starting floor and the requested floor.

1. index.js

• Main file that uses these classes. Remember to require the other files in this file.

Most of the functions we need to create will be in elevator.js, so let's begin there.

The Elevator class

First, the elevator needs methods to move. We will take care of what triggers the movement later.

In order to make it move, it will need a direction and a current position (floor). Let's focus on four main methods:

• The update function should (for now) display the current status of the elevator by calling the log function.
• The log function should just print the information related with position and direction:

Direction: up | Floor: 0

• The start function should start a setInterval call the update function every second
• The stop function should stop the elevator's setInterval listening for requests

These last two functions are key to the exercise.

Remember to use JavaScript functions such as setTimeout() to create the listener

Iteration 2

In the second iteration, the elevator should move up and down depending on its direction and the future passengers' requests.

Write the code for the floorUp function to update the current floor by incrementing it by one. So, if the current floor was 0, it will become 1. If it's 3, it should become 4.

Then, write the code for floorUp's sister function, floorDown. It should update the current floor by subtracting one from the current floor. So, if the current floor was 6, it will become 5.

Remember to consider the limits of the elevator so it doesn't go higher than the top floor or below the ground floor.

Test the elevator. Make it go to the top floor and the ground floor by using floorUp and floorDown. Display its status in the console with the log method.

Test what happens when you go past the top floor and below the ground floor.

Iteration 3

Elevators pick up and drop off passengers, so we will have to represent those passengers in our program. Let’s use our class Person to describe passengers.

The Person class

A person should have three attributes:

• A name
• A originFloor: the floor they are in when they call the elevator
• A destinationFloor: the floor they intend to go to

Now, we need to think about what happens when a person ‘calls’ the elevator. In the Elevator class, it's time to write the code for the call method. This method should receive a person object and add it as a request into the elevator’s queue.

Add the whole person object to the requests array. The elevator will need all that information later.

In later iterations, the elevator will process the list of requests as it travels up and down. We will need a list of floors that the elevator should serve in the update method.

Iteration 4

When elevators travel up and down, it has to pick up people so that they can enter the elevator.

To keep a track of everyone, you will have three different lists:

• waitingList: people waiting for the elevator -they made the request and they're waiting the elevator to come
• passengers: people currently in the elevator
• requests: a list of pending requests. Floors where the elevator must stop.

The Waiting List

When a person calls the elevator (the call function is executed), we will add that person into the waitingList array. Notice they're not in the passengers collection because they're not yet in the elevator.

Also, add the (originFloor) to the requests array to let the elevator know where it has to stop to pick the passenger up.

A passenger enters the elevator

When the elevator arrives to any floor, it should check the waitingList array to verify if a person is waiting there. If this condition occurs:

• add the person into the passengers array
• delete the passenger from the waitingList
• Add the destination floor of the passenger to the elevator requests

We will show a message to indicate what just happens:

Julia has enter the elevator

A passenger leaves the elevator

When the elevator arrives to a floor, it should check the passengers collection. If a passenger's destinationFloor matches the current floor:

• we will delete that person from the passengers array.

We will show a message to indicate what just happens:

Julia has left the elevator

Good luck!

Extra resources

• The Elevator Saga
• Codepen - Ok, we're in the backend, right? But this is a pretty simulation 😝