Implementation of Pascal Triangle using Recursive Function - JavaScript ES6

pascalTriangleRecursive.js

const pascalTriangleRecursive = (n, arr) => {
  if (!arr) arr = [[1]] // Create triangle
  if (n < 2) return arr // Exit

  const prevLine = arr[arr.length - 1] // Get previous line

  const newLine = [1] // Create new line

  // Populate new line
  prevLine.forEach((item, index) => {
    if (index === 0) return
    if (index === prevLine.length) return
    newLine.push(prevLine[index] + prevLine[index - 1])
  })

  newLine.push(1) // Finalise new line

  arr.push(newLine) // Insert new line to triangle

  return pascalTriangleRecursive(n - 1, arr) // Invoke itself passing the counter and array
}