select2全选和全部取消

全选

$(".all-checked").click(function(){
    var arr = [];
    $(".departments option").each(function(){
        arr .push($(this).val());
    })
    
    $(".departments").val(arr );
    $(".departments").trigger("change");
});

取消全选

$(".all-unchecked").click(function(){
    $(".departments").val(null).trigger("change");
});