After this lesson, you will be able to:

• Develop some basic TypeScript functions.
• Create a TypeScript interface, and use it from a class.
• Implement two different interfaces and use them from classes.

• Fork this repo.
• Clone this repo into your ~/code/labs folder.
• Install TypeScript on your computer

  $ npm install -g typescript
  

• It's recommended to install the atom-typescript extension.

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 "-"

When we are studying, it's very common to create lists to remember different things: finish exercises, create a pull-request with the solution, eat, sleep... some of them are more important than others, but we have to remember all of them.

We are going to help you with this. How? We are going to create a ToDo list project in TypeScript. We are going to create different lists following different strategies with TypeScript. In the process, we will cover several important basic topics: variable types, functions, classes, and interfaces.

The project structure will be as follows:

starter-code/
├── iteration-1
│   ├── index.html
│   ├── main.js
│   └── main.ts
├── iteration-2
│   ├── index.html
│   ├── main.js
│   ├── main.ts
│   ├── todointerfaces.js
│   └── todointerfaces.ts
└── iteration-3
    ├── index.html
    ├── main.js
    ├── main.ts
    ├── interfaces.js
    └── interfaces.ts

You are going to work over the *.ts files in the different folders, one for each iteration that we are going to cover.

Note: Remember that the *.js files are generated every time we save the TypeScript files in our solution.

In the first iteration of the exercise, we are going to create our To-Do list using functions. Let's consider what we need to implement all the necessary functions for our list.

First of all, we need to be able to save the tasks we have to do. In order to do this, we will need somewhere to store them. We will use an array. With this array we will be able to:

• Add a new task (a string).
• Remove a task that we've completed.
• Iterate over all the tasks so that we can see them.

Each of these features is a function that we will have to create. To add and remove tasks, we will need to specify as a parameter the string for the task itself ("Buy eggs", for example).

Once we have inserted or removed the task, we should return the number of elements that are in the list. We should also print the following in the console:

For adding a task

=========== NEW TASK ===========
Task "Buy eggs" inserted in the list
Number of items: 1

For removing a task

=========== TASK REMOVED ===========
Task "Buy eggs" removed from the list
Number of items: 0

In both cases, "Buy eggs" is the text of the task we just inserted/deleted.

Example: If the first task we add is "Start working with TypeScript", the output should be the following:

=========== NEW TASK ===========
Task "Start working with TypeScript" inserted in the list
Number of items: 1

We also need a function to list all of our tasks. For this function, we just need to print in console all the items in our array. This function doesn't need a return value.

Once you have implemeneted all these features, you will have the first iteration completetd.

Tasks

• Create an array of strings.
• Create an addTask function:
  • It receives a string as a parameter called task.
  • It adds the task to the array.
  • It prints a message indicating the insertion.
  • It returns the number of elements in the list and prints that number in the console as well.
• Create a listAllTasks function:
  • It iterates over all the tasks in the list.
  • It prints each list item in the console.
• Create a deleteTask function:
  • It receives a string as a parameter called task.
  • It removes that string from the array.
  • It returns the number of elements in the list after the deletion.
  • It prints a message indicating the deletion.
  • It returns the number of elements in the list and prints that number in the console as well.

In this iteration we are going to implement the same functionality by using an Interface. We are going to be working with the iteration-2 folder.

Remember that an interface specifies all the functions that a class will have, and also the parameters of each function.

We will create an Interface in the todointerface.ts file that will specify the different properties and methods described in the first iteration:

• An Array of tasks.
• A function to add tasks that will receive the task as a parameter.
• A function to list all the tasks.
• A function to delete tasks that will receive the task as a parameter.

Once we have defined and exported the Interface, we will create a class called Todo that will implement the interface and its methods. We are going to add this class in the main.ts file.

We have to keep the same inputs and outputs we have used in the previous iteration.

Tasks

Interface (todointerface.ts)

• Array of strings.
• addTask function:
  • It receives a string as a parameter
  • It returns a number.
• listAllTasks function:
  • It has no parameters.
  • It doesn't return anything.
• deleteTask function:
  • It receives a string as a parameter
  • It returns a number.

Class (main.ts)

• Create a class that implements the Interface:
• Remember that you need to import the interface before you use it.
• Implement all the properties and functions indicated in the interface:
• Create an array of strings.
• Create an addTask function:
  • It receives a string as a parameter.
  • It prints the same message as iteration 1.
  • It returns the number of elements in the list and prints this number to the console as well.
• Create a listAllTasks function:
  • It prints in console all the tasks of the list.
  • It doesn't return anything.
• Create a deleteTask function:
  • It receives a string as a parameter.
  • It prints the same message as iteration 1.
  • It returns the number of elements in the list and prints the number in the console also.

To finish up with this exercise, we are going to create the same Todo list by adding another interface (and class) to our implementation. In the final iteration, we will be working with the code in the iteration-3 folder.

When we have different elements in a project, it's very common (and also a good practice) to treat each of them as an independent element and create a class and interface for each of these elements. In this case, we have been creating a Todo list without considering the possibility of splitting that into two different parts: the list, and the items.

In this iteration, we are going to create two different interfaces, one for the list elements, and another one for the list itself. So inside the list, we are going to have a reference to the other interface.

The list item interface will have the following properties:

• Title of the task, which will be a string.
• Status of the task, represented by a boolean value.
• Updated At, that will store the date when the task was last modified.
• Toggle Status function, which will set the status as true if it's false, and viceversa.

In the Todo list interface, we will have the following properties:

• An array of list item elements.
• A function to add a task, which will receive the TodoItem as a parameter.
• A function to list all the items in the list.
• A function to delete a task, which will receive the TodoItem as a parameter.

Once we have implemented both interfaces, we will have to create the classes that will implement them. In the main.ts file, we will add a TodoItem class, which should implement the TodoItemInterface, and the TodoList class, which should implement the TodoListInterface interface.

Once you are done with that, the exercise will be finished!

Tasks

Interfaces (interfaces.ts)

• TodoItemInterface
  • Define a title as string.
  • Add a status as a boolean.
  • updatedAt is a Date that represents when the task was last updated.
  • Add a function called toggleStatus that will update the task status.
• TodoListInterface
  • Define an Array of TodoItems.
  • Create an addTask function:
    • It receives a TodoItem as a parameter.
    • It returns the number of elements in the list and prints the number.
  • Add a listAllTasks function:
    • It doesn't return anything.
    • It lists all the titles of all the TodoItems in the list
  • Create a deleteTask function:
    • It receives a TodoItem as a parameter.
    • It returns the number of elements in the list and prints the number.

Class (main.ts)

• Create a TodoItem class that implements the TodoItemInterface interface, adding all the required properties and functions specified in the interface:

  • title string field, to indicate what the task entails.
  • status that will indicate if the task is completed or not.
  • updatedAt date field, to indicate the date that the task was last updated.
  • We have to add a constructor to the class to set up the task title and the updatedAt values when creating a task.
  • toggleStatus function to change the status of a TodoItem. It should:
    • Change the status of the task. If the status is currently 'finished', the new status will be 'unfinished', and viceversa.
    • Update the updatedAt value, by setting up the current date.
    Without supplying a parameter, how can you accomplish this with a simple function?

• Create a TodoList class that implements the TodoListInterface interface, adding all the required properties and functions specified in the interface:

  • An Array of TodoItems to be able to save the different tasks you want to do.
  • Create an addTask function:
    • It receives a string as a parameter.
    • It prints in console the same message as iteration 1.
    • It returns the number of elements in the list and prints the number.
  • Create a listAllTasks function:
    • It prints all the tasks of the list. In this case, we want to print the title and the updated date of the task.
    • It doesn't return anything.
  • Create a deleteTask function:
    • It receives a string as a parameter.
    • It prints in console the same message as iteration 1.
    • It returns the number of elements in the list and prints the number.

Happy coding!

Typescript Documentation