task.js

//1. A function which prints str after n seconds.
function printTimeout(str, n) { 
  setTimeout(() => console.log(str) , n * 1000);
}
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) { 
 if (n != 1) {
        return n + sumAll(n - 1);
    }
    else return n;
}
console.log(sumAll(2)); // 3
console.log(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) {
    if (time == 0) {
        console.log(str);
    } else {
        let intervalId = setInterval(function () {
            if (time >= 1) {
                console.log(time--);
            };
        }, 1000);
        setTimeout(function () {
            clearInterval(intervalId);
            console.log(str);
        }, (time + 1) * 1000);
    }
}

bombTimer('Boooom', 3);


//4. A function which returns factorial of number using recursion.
function factorial(n){ 
 if (n == 0) { return 1; }
  else {
    if (n != 1) {
      return n*factorial(n-1);
    }
    else return n; 
  }
}
console.log(factorial(3)); // 6
console.log(factorial(5)); // 120


//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) { 
 return arr.filter(function (item) {
      return item <= maxNumber;
    });     
}
filterNumbers([1, 4, 8, 1, 20], 5) // [1, 4, 1]


//9. A function which concats all first-nested arrays in one array (use reduce):
function concatFirstNestedArrays(arr) 
{ 
    return arr.reduce((a, b) => a.concat(b));
 }
  concatFirstNestedArrays([[0, 1], [2, 3], [4, 5]]) // [0, 1, 2, 3, 4, 5]