Step 2.1 - Introduction to TypeScript (Exercise)

Lessons | Demo | Final

If you don't already have the app running, start it by running npm start from the root of the frontend-bootcamp folder.

Exercises will be completed under this step's exercise/src folder unless otherwise noted. You'll also want to open the Step2-01 exercise page to see the results as you work.

Modules

1. Open the file exercise/src/fibonacci.ts in VS Code

2. Inside this file, write a function called fib(n) that takes in a number and returns the n-th Fibonacci number (be sure the specify the type of n).

HINT: function fib(n: number) { return n <= 1 ? n : fib(n - 1) + fib(n - 2); }

3. Export fib(n) as a named export

4. Export a const variable FibConst as a default export

5. Inside index.ts in the same folder, import both fib and FibConst, and use the built-in console.log() function to log the result of fib(FibConst).

Types and interfaces

Inside exercise/src/index.ts:

1. Add a type alias for string union type describing the states of Red-Green-Yellow traffic light: type TrafficLight = ???

2. Describe a type of car with an interface: interface Car { ... } complete with wheels, color, make, model

3. Create a valid car instance and log it using console.log(): const myCar: Car = { ??? };

Generics

Inside exercise/src/stack.ts, create a generic class for a Stack<T> complete with a typed pop() and push() methods.

Hint: the JavaScript array already has push() and pop() implemented for you. That can be your backing store.

In exercise/src/index.ts, create a Stack<number> and use console.log() to demonstrate its functionality.

Spread and destructuring

1. Note the following code in index.ts:

const obj1 = {
  first: 'who',
  second: 'what',
  third: 'dunno',
  left: 'why'
};

const obj2 = {
  center: 'because',
  pitcher: 'tomorrow',
  catcher: 'today'
};

2. Now create a one-liner using the spread syntax {...x, ...y} to create a new variable megaObj that combines these two objects.

3. Use the destructuring syntax to retrieve the values for {first, second, catcher} from megaObj.

Async / await

Note the following code in index.ts:

function makePromise() {
  return Promise.resolve(5);
}

1. Call makePromise() with the await syntax and log the results.

2. Create a new function that uses the async keyword. Inside the function, make an await call to makePromise() and return the results.