Pascal's Triangle

pascalstriangle.js

var generate = function(numRows) {
  if (numRows === 0) { return []; }
  var pascalsTriangle = [[1]];
  
  for (let i = 1; i < numRows; i++) {
    var last = pascalsTriangle[pascalsTriangle.length - 1];
    var newLevel = []; 

    for (let j = 0; j <= last.length; j++) {
      var previous = last[j - 1];
      var current = last[j];
      if (j === 0 || j === last.length) {
        newLevel.push(1);
      } else {
        newLevel.push(current + previous);
      }
    }
    pascalsTriangle.push(newLevel);
  }
  
  return pascalsTriangle;
};