Bootstrap mobile menu icon change to x close

Question

EDIT

@zim answer uses 2020 CSS to easily solve the issue and better applies to Bootstrap 4.

The original question and selected answer are still

Answer 1

Smart decision helped me in codepen

HTML

CSS

.navbar-toggle .icon-bar:nth-of-type(2) {
    top: 1px;
}
.navbar-toggle .icon-bar {
    position: relative;
    transition: all 500ms ease-in-out;
}
.navbar-toggle.active .icon-bar:nth-of-type(1) {
    top: 6px;
    transform: rotate(45deg);
}
.navbar-toggle.active .icon-bar:nth-of-type(2) {
    background-color: transparent;
}
.navbar-toggle.active .icon-bar:nth-of-type(3) {
    top: -6px;
    transform: rotate(-45deg);
}

JS

$(".navbar-toggle").on("click", function () {
    $(this).toggleClass("active");
});