function steps(n) {

  for (let row = 0; row < n; row++) {

    let stair = "";

    for (let column = 0; column < n; column++) {

      if (column <= row) {

        stair += "#";

      } else {

        stair += " ";

      }

    }

    console.log(stair);

  }

}

​

steps(4)

function steps2(n, row = 0, stair = "") {

  if (n === row) {

    return;

  }

​

  if (n === stair.length) {

    console.log(stair);

    steps2(n, row + 1);

    return;

  }

​

  if (stair.length <= row) {

    stair += "#";

  } else {

    stair += " ";

  }

  steps2(n, row, stair);

}

​

steps2(4)