Pascal's triangle interview q

pascals.js

var generate = function(numRows) { 
  if (numRows === 0) { 
    return [];
  }
  var output = [[1]];
  if (numRows === 1) {
    return output;
  }
  for (var i = 0; i < numRows; i++) {
    var last = [];
    output.forEach(function(prev) {
      last[0] = prev[0];
      for (var i = 0; i < prev.length; i++) {
        if (prev[i + 1] === undefined) {
          last[i + 1] = prev[i];
        } else {
          last[i + 1] = prev[i] + prev[i + 1];
        }
      } 
      output.push(last)
    });
  } 
  return output;
};