A simplest method to solve Hackerrank stairCase problem.

stair-case.js

function stairCase(n){
    let arr = Array(n-1).fill(' ')
    
    for (let i = n-1; i >= 0; i--) {
        arr[i] = '#';
        console.log(arr.join(''));
    }
}

stairCase(6)

it works