How to iterate through jQuery UI selectmenu by using 2 buttons?

Question

Please try the jsFiddle with jQuery UI selectmenu and 2 buttons.

With the help of 2 buttons prevGame and nextGame I am able to change the selectedIndex variable tracking the currently selected game number.

The jQuery UI selectmenu doc unfortunately does not explain how to set and get (so that I can update the span currGame) the currently selected item:

Please explain: how to set and get the selected item in jQuery UI selectmenu?

HTML-code:

<form>
  <select name="games" id="games"></select>
  <button id="prevGame">&lt;</button>
  <span id="currGame">Loading...</span>
  <button id="nextGame">&gt;</button>
</form>

JavaScript-code:

var yourGames = [1, 3, 5];
var hisGames = [8, 10, 12, 14];
var selectedIndex = 0;

$("#games").selectmenu();

// emulate repeating server responses
setInterval(function() {
  updateMenu();
}, 5000);

$('#prevGame').button().click(function(e) {
  e.preventDefault();
  selectedIndex = Math.max(selectedIndex - 1, 0);
  updateButtons();
});

$('#nextGame').button().click(function(e) {
  e.preventDefault();
  selectedIndex = Math.min(selectedIndex + 1, lastIndex());
  updateButtons();
});

function lastIndex() {
  return yourGames.length + hisGames.length - 1;
}

function updateButtons() {
  $('#currGame').html('selectedIndex=' + selectedIndex); // TODO: change to "Game #"
  $('#prevGame').button(selectedIndex == 0 ? "disable" : "enable");
  $('#nextGame').button(selectedIndex == lastIndex() ? "disable" : "enable");
}

function updateMenu() {
  var yourGroup = ['<optgroup label="YOUR TURN">'];
  for (var i = 0; i < yourGames.length; i++) {
    var gameNumber = yourGames[i];
    var selectedTag = (i == selectedIndex ? 'selected="selected"' : '');
    yourGroup.push(
      '<option ' +
      selectedTag +
      ' value="' +
      gameNumber +
      '">Game #' +
      gameNumber +
      '</option>');
  }
  yourGroup.push('</optgroup>');

  var hisGroup = ['<optgroup label="HIS TURN">'];
  for (var i = 0; i < hisGames.length; i++) {
    var gameNumber = hisGames[i];
    var selectedTag = (i - yourGames.length == selectedIndex ? 'selected="selected"' : '');
    hisGroup.push(
      '<option ' +
      selectedTag +
      ' value="' +
      gameNumber +
      '">Game #' +
      gameNumber +
      '</option>');
  }
  hisGroup.push('</optgroup>');

  $("#games").selectmenu('destroy')
    .empty()
    .append(yourGroup.length > 2 ? yourGroup.join('') : '')
    .append(hisGroup.length > 2 ? hisGroup.join('') : '')
    .selectmenu(); // TODO: select the game at selectIndex
}

UPDATE:

I have prepared a newer jsFiddle using selectmenu("refresh") instead of selectmenu("destroy"), but it still has some issues.

Answer 1

jQuery and jQuery UI provides no way to directly set selected index of a select menu. You can use pure javascript way to set the selected index. Also I assume you want to change the text between buttons every time select menu changes. You can do it like so:

var yourGames = [1, 3, 5];
var hisGames = [8, 10, 12, 14];
var selectedIndex = 0;

setInterval(function() {
  updateMenu();
  updateCurrentGame();
  updateButtons();
}, 5000);

$("#games").selectmenu();

$('#prevGame').button().click(function(e) {
  e.preventDefault();
  selectedIndex = Math.max(selectedIndex - 1, 0);
  updateButtons();
  updateCurrentGame();
});

$('#nextGame').button().click(function(e) {
  e.preventDefault();
  selectedIndex = Math.min(selectedIndex + 1, lastIndex());
  updateButtons();
  updateCurrentGame();
});

function lastIndex() {
  return yourGames.length + hisGames.length - 1;
}

function updateButtons() {
  $('#prevGame').button(selectedIndex == 0 ? "disable" : "enable");
  $('#nextGame').button(selectedIndex == lastIndex() ? "disable" : "enable");
}

// Update the select menu when prev & next buttons are pressed
function updateCurrentGame() {
  var selectedText = $($("select#games option")[selectedIndex]).text();
  $('#currGame').html(selectedText);
  // pure js vay to set selected index
  $("#games")[0].selectedIndex = selectedIndex;
  $("#games").selectmenu("refresh");
}

// Update the selected index every time the select menu is changed manually
$("#games").on("selectmenuchange", function(e, ui) {
  console.log(ui);
  selectedIndex = ui.item.index;
  var selectedText = ui.item.element.text();
  $('#currGame').html(selectedText);
  updateButtons();
})

function updateMenu() {
  var yourGroup = ['<optgroup label="YOUR TURN">'];
  for (var i = 0; i < yourGames.length; i++) {
    var gameNumber = yourGames[i];
    var selectedTag = (i == selectedIndex ? 'selected="selected"' : '');
    yourGroup.push(
      '<option ' +
      selectedTag +
      ' value="' +
      gameNumber +
      '">Game #' +
      gameNumber +
      '</option>');
  }
  yourGroup.push('</optgroup>');

  var hisGroup = ['<optgroup label="HIS TURN">'];
  for (var i = 0; i < hisGames.length; i++) {
    var gameNumber = hisGames[i];
    var selectedTag = (yourGames.length + i == selectedIndex ? 'selected="selected"' : '');
    hisGroup.push(
      '<option ' +
      selectedTag +
      ' value="' +
      gameNumber +
      '">Game #' +
      gameNumber +
      '</option>');
  }
  hisGroup.push('</optgroup>');

  $("#games").selectmenu('destroy')
    .empty()
    .append(yourGroup.length > 2 ? yourGroup.join('') : '')
    .append(hisGroup.length > 2 ? hisGroup.join('') : '')
    .selectmenu();
}

button#prevGame,
span#currGame,
button#nextGame,
button#newGame {
  vertical-align: top;
}
select#games {
  width: 300px;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

<script src="https://ajax.googleapis.com/ajax/libs/jqueryui/1.11.4/jquery-ui.min.js"></script>
<link href="https://ajax.googleapis.com/ajax/libs/jqueryui/1.11.4/themes/smoothness/jquery-ui.min.css" rel="stylesheet" />

<form>
  <select name="games" id="games"></select>
  <button id="prevGame">&lt;</button>
  <span id="currGame">Loading...</span>
  <button id="nextGame">&gt;</button>
</form>