print-diagonal.js

var input = [
  [1, 2, 3],
  [4, 5, 6],
  [7, 8, 9]
];

var output = [
  [1],
  [4, 2],
  [7, 5, 3],
  [8, 6],
  [9]
];

var columns = input[0].length;
var rows = input.length;
var result = [];

for (var index = 0; index < (rows + columns); index++) {
  var i = index < rows ? index : rows - 1;
  var j = index < rows ? 0 : (index - rows + 1);

  while (i >= 0 && j < columns) {
    result[index] = result[index] || [];
    result[index].push(input[i--][j++]);
  }
}

result.forEach(function(row) {
  console.log(row.map(function(v) {
    // if (v < 10) {
    //   return " " + v;
    // }
    return v;
  }).join("  "));
});