pascal's triangle in javascript

pascals-triangle.js

function pt(lineLimit, lines) {
  // Seed the first value.
  if(!lines || lines.length === 0) return pt(lineLimit, [[1]]);

  var newLine = [];
  var lastLine = lines[lines.length - 1];

  // Fill out inner values
  for(var i=1, len=lastLine.length; i<len; i++) {
    newLine.push(lastLine[i - 1] + lastLine[i]);
  }

  // Add 1s border to both sides.
  newLine.unshift(1);
  newLine.push(1);

  // Add the new line to the lines array.
  lines.push(newLine);

  if(lineLimit === lines.length) {
    // Finished!
    return lines;
  } else {
    // Generate the next line.
    return pt(lineLimit, lines);
  }
}

pt(5);

/*

Output:
[
  [ 1 ],
  [ 1, 1 ],
  [ 1, 2, 1 ],
  [ 1, 3, 3, 1 ],
  [ 1, 4, 6, 4, 1 ]
]

*/