pascalTriangle.js

function centerString(string, distance) {
  const spaces = ' '.repeat(distance)
  return spaces + string + spaces
}

function calculateTriangle(n, a = [[1]]) {
  if (n < 2) {
    return a
  }

  const previousRow = a[a.length - 1]
  const currentRow = [1]

  for (let i = 1; i < previousRow.length; i++) {
    currentRow[i] = previousRow[i] + previousRow[i - 1]
  }

  currentRow.push(1)
  a.push(currentRow)

  return calculateTriangle(n - 1, a)
}

function buildPascalTriangle(n) {
  const triangle = calculateTriangle(n)

  let str = ''
  let last = triangle[triangle.length - 1].join(' ')

  for (let i = 0; i < triangle.length - 1; i++) {
    const numbers = triangle[i].join(' ')

    str += centerString(numbers, (last.length - numbers.length) / 2) + '\n'
  }

  str += last
  return str
}

const d = buildPascalTriangle(10)
console.log(d)