After writing tic-tac-toe, there were some subtle improvements possible, HW was assigned and these are the answers

gistfile1.js

//1) Fix computer algorithm (assigning to Anth)
// In Player's .makeMove method:
if (index == null) {
  // No block?  Try for center...
  //console.log('computer is attempting to center');
  if (grid.vectors[4].value == null) {
    index = 4;
  }   
} 



//2) Add start-of-game ability to set up human v human, human v computer, or computer v computer (assigning to Dan)
Game.prototype.setUpPlayers = function() {
  console.log('Choose your player option: 1 for human v human, 2 for human v computer, 3 for computer v computer');
  var invalidMove = true;
  while (invalidMove) {
    var choice = parseInt(prompt('Enter a number: ')); 
    if ([1,2,3].indexOf(choice) > -1) {
      if (choice == 1) {
        this.players = [new Player('human', 'X'), new Player('human', 'O')]
      }
      else if (choice == 2) {
        this.players = [new Player('human', 'X'), new Player('computer', 'O')] 
      }
      else {
        this.players = [new Player('computer', 'X'), new Player('computer', 'O')]
      }
      invalidMove = false;
    }
    else {
      console.log("Please enter a valid number");
    }
  }
}

Game.prototype.play = function() {
  console.log('Welcome to Tic-Tac-Toe!\n' +
    'To move, Enter a number from 1-9 when prompted.');
  this.setUpPlayers();
  //...



  
//3)  Add a console log that informs the player of all of their possible remaining moves at the start of their turn (assigning to Rod)
// In Player's .makeMove method, under if human:
  if (this.type == 'human') {
    open_indexes = grid.vectors.filter(function(vector) {
      return vector.value == null;
    }).map(function(vector, i) {
      return grid.vectors.indexOf(vector)+1;
    });
    while (invalidMove) {
      var index = prompt('Enter a number from this list of available spaces ' + open_indexes + ': ') - 1;