43-js-essentials-homework.md

Homework

Do at least 5 tasks.

1. A function which prints str after n seconds.

function printTimeout(str, n) { /* your code */ }
printTimeout('hello', 10) // hello will appear after 10secs in console

2. A function which returns sum of all numbers from 1 to n using recursion.

function sumAll(n) { /* your code */ }
sumAll(2); // 3
sumAll(4); // 10

3. A function which takes str and time in seconds as arguments, then every second it should count down from time to 0 and print current time to console when time equals to 0 it prints str

function bombTimer(str, time) { /* your code */ }
bombTimer('Boooom', 3);
3
2
1
Boooom

4. A function which returns factorial of number using recursion.

function factorial(n) { /* your code */ }
factorial(3); // 6
factorial(5); // 120

5. Implement function from task №3 (bombTimer) using recursion and setTimeout.

6. A function which takes an array of numbers and maxNumber, the function returns new array with numbers not higher than maxNumber.

function filterNumbers(arr, maxNumber) { /* your code */ }
filterNumbers([1, 4, 8, 1, 20], 5) // [1, 4, 1]

7. A function that returns object with min and max numbers from array of numbers.

function minMax(arr) { /* your code */ }
minMax([1, 4, 8, 2, 20]) // { max: 20, min: 1 }

8. A function that returns average of numbers in array.

function average(arr) { /* your code */ }
average([1,4,2]) // 2.33

9. A function which concats all first-nested arrays in one array (use reduce):

function concatFirstNestedArrays(arr) { /* your code */ }
concatFirstNestedArrays([[0, 1], [2, 3], [4, 5]]) // [0, 1, 2, 3, 4, 5]

10. A function accepts array of users and returns object of users where key is user id and value user data.

const users = [
  { id: 1, name: 'John', birthday: '1999-2-12' },
  { id: 2, name: 'Bill', birthday: '1999-1-19' },
  { id: 3, name: 'Carol', birthday: '1999-3-11' },
  { id: 4, name: 'Luce', birthday: '1999-2-22' }
];

function usersToObject(users) { /* your code */ }
usersToObject(users)
// {
//  1: { id: 1, name: 'John', birthday: '1999-2-12' },
//  2: { id: 2, name: 'Bill', birthday: '1999-1-19' },
//  3: { id: 3, name: 'Carol', birthday: '1999-3-11' },
//  4: { id: 4, name: 'Luce', birthday: '1999-2-22' }
// };

11. A function returns array of users that have birthdays in a specific month.

const users = [
  { name: 'John', birthday: '1999-2-12' },
  { name: 'Bill', birthday: '1999-1-19' },
  { name: 'Carol', birthday: '1999-4-11' },
  { name: 'Luce', birthday: '1999-2-22' }
];

function filterUsersByMonth(users, month) { /* your code */ }
filterUsersByMonth(users, 0) // [{ name: 'Bill', birthday: '1999-1-19' }]

12. A function returns name and age of users separated by comma that are older than 18.

const users = [
  { name: 'John', birthday: '1999-6-12' },
  { name: 'Bill', birthday: '2005-5-19' },
  { name: 'Carol', birthday: '2003-10-11' },
  { name: 'Luce', birthday: '2000-11-22' }
];

function getAdultNames(users) { /* your code */ }
usersToString(users) // 'John 19, Luce 18'