I am trying to animate open (+) and close (x) buttons for main navigation. It's not working properly and I am getting this error.
Uncaught TypeError: Cannot read property 'addEventListener' of null
JavaScript
document.querySelector( "#nav-toggle" ).addEventListener( "click", function() {
this.classList.toggle( "active" );
});
HTML
<a id="nav-toggle" href="#navi" data-toggle="collapse"
data-target="#bs-example-navbar-collapse-1">
<span></span>
</a>