browser_grocery_list.js

function newList() {
  var listString = prompt("Welcome to GroceryListMaker!\n\n" + 
        "Enter items with quantities like so:\n"
        + "2 apples, 1 tomato, 3 pomegranates, 1 sugar");
  var list = {};

  listString = listString.split(", ");
  for (var i=0; i < listString.length; i++) {
    var quant = listString[i].split(" ")[0];
    var item = listString[i].split(" ")[1];
    list[item] = quant;
  }

  while (true) {
    var stringToPrint = "";
    for (var elem in list) {
      stringToPrint += list[elem] + " " + elem + "\n";
    }

    var answer = prompt(stringToPrint + 
          "\n\nWant to update quantities or add items? type \"update\"" +
          "\nWant to delete items? type \"delete\"")

    if (answer.toLowerCase().includes("delete")) {
      var toDelete = prompt(stringToPrint + 
        "\n\nWhich item or items would you like to delete from your list?\n"
        + "Enter all the items to delete with spaces between, like this:\n" + 
        "apples oranges");
      toDelete = toDelete.split(" ");
      for (var j=0; j < toDelete.length; j++) {
        delete list[toDelete[j]];
      }
    } else if (answer.toLowerCase().includes("update")) {
      var toUpdate = prompt(stringToPrint + 
        "\n\nWhich item or items quantities would you like to update?"
        + "\nEnter all the items to update with new amounts," + 
        "and spaces between them, like this:\n" +
        "\n1 apples, 3 oranges\n" + 
        "\nYou can add new items to the list in the same way." );
      toUpdate = toUpdate.split(", ");
      for (var j=0; j < toUpdate.length; j += 2) {
        var newQuant = toUpdate[j].split(" ")[0];
        var item = toUpdate[j].split(" ")[1];
        list[item] = newQuant;
      }
    } else {
      break;
    }
  }

  alert("Here's your final list!\n\n" + stringToPrint);
  return list;
}