Use below code.
function PopulateDropDown(dropDownId, list) {
var modal = $('<div />');
modal.addClass("modalBackground");
$('body').append(modal);
var loading = $(".loading");
loading.show();
var top = Math.max($(window).height() / 2 - loading[0].offsetHeight / 2, 0);
var left = Math.max($(window).width() / 2 - loading[0].offsetWidth / 2, 0);
loading.css({ top: top, left: left });
setTimeout(function () {
if (list != null && list.length > 0) {
$(dropDownId).removeAttr("disabled");
$.each(list, function () {
$(dropDownId).empty().append('<option selected="selected" value="0">Please select</option>');
$(dropDownId).append($("<option></option>").val(this['Value']).html(this['Text']));
});
$(".loading").hide();
$('.modalBackground').remove();
}
}, 1000);
}