purlo_questions.js

/*
* QUESTION 1:
* Write a code snippet that would transform "animalCollective" into "expected"
*/

const animalCollective = [
  {type: 'dog', name: 'bobi'}, 
  {type: 'fish', name: 'glup'}, 
  {type: 'fish', name: 'glup the second'}, 
  {type: 'cat', name: 'Aaron'}
];

const expected = { 
  fish: [
    {type: 'fish', name: 'glup'}, 
    {type: 'fish', name: 'glup the second'}
  ], 
  cat: [{type: 'cat', name: 'Aaron'}], 
  dog: [{type: 'dog', name: 'bobi'}] 
} 

/*
* QUESTION 2:
* What's the value of "arrayOfStrings" after evaluation ? Why ?
*/

const arrayOfStrings = ['a', 'b', 'c'].forEach(v => 'a');

/*
* QUESTION 3:
* What's the value of "anotherArrayOfStrings" after evaluation ? Why ?
*/

const anotherArrayOfStrings = ['a', 'b', 'c'].map(v => 'a');

/*
* QUESTION 4:
* What's the value of "ben" and "userNames" after the evaluation of the following snippet ? Why ?
*/

const ben = {name: 'Ben', age: 2 };
const tom = {name: 'Tom', age: 3 };

const users = [ben, tom];
const userNames = users.map(user => user.name).join();

/*
* QUESTION 5:
* What's the value of "ben" and "myNames" after the evaluation of the following snippet ? Why ?
*/

const ben = {name: 'Ben', age: 2 };
const tom = {name: 'Tom', age: 3 };

const users = [ben, tom];

const myNames = users.map(user => {
  user.name = `My name is ${user.name}`;
}).join();

/*
* QUESTION 6:
* Name 1 advantage and 1 disavantage of using immutable datastructures.
*/

/*
* QUESTION 7:
* Given that we are using RxJS. What will be printed to the console when the following snippet runs ? 
*/
import { Subject } from 'rxjs';
import { scan } from 'rxjs/operators';

const actionDispatcher = new Subject();
const state$ = actionDispatcher.asObservable().pipe(scan((currentState, action) => {
  switch(action.type) {
    case 'reset':
      return action.payload
    case 'add':
      return action.payload + currentState
  }
  
  throw new Error('Unkown action type');
}, 0));

state$.subscribe(state => console.log(state));

actionDispatcher.next({type: 'add', payload: 1});
actionDispatcher.next({type: 'add', payload: 2});
actionDispatcher.next({type: 'reset', payload: 0});
actionDispatcher.next({type: 'add', payload: 3});

/*
* QUESTION 8:
* Rewrite the snippet on question 8 to use Typescript. If you don't know RxJS typings rewrite question 1.
*/

/*
* QUESTION 9:
* What is the difference between type checking at compiletime and type checking runtime ? 
* Which kind of type checking is used by typescript ? Which kind of type checking is used by javascript ?
*/