First and Last K Numbers JS Fundamentals

firstAndLastKNumbers([2, 7, 8, 9]);

function firstAndLastKNumbers(arr) {
    let k = arr.shift(); // (3) [7, 8, 9]
    // k = 2 - the removed element from the original array

    let firstLine = arr.slice(0, k) // (2) [7, 8];
    // k shows the count of numbers per line

    let secondLine = arr.slice(arr.length - k, arr.length); // (2) [8, 9]
    // arr.length - k = 3 - 2 = 1 -- the start index of slice function which is 8

    console.log(firstLine.join(' '));
    console.log(secondLine.join(' '));
}