how to select and deselect all options in a select box

Answer 1

Somehow the answers above did not work for me. Seems that you have to use properties instead of attributes. Here is the code:

$('#selectall').click(function() {
    $('select#studentremain option').prop("selected",true);
});   

$('#deselectall').click(function() {
    $('select#studentremain option').prop("selected",false);
});

Documentation says that selected attribute only specifies that an option should be pre-selected when the page loads. But is not set when the actual option is selected by the user. Source