Show slow not working iphone IOS

[tiagocaus]

Good morning everyone. Why does this code below work on the browser, android, but does not work on IOS?

$(document).ready(function() {
    $("#menuIco").on("click touchstart", function() {
        if ($('#menuNav').is(':hidden')) {
            $('#menuNav').show('slide', {direction: 'left'}, 400);
        } else {
            $('#menuNav').hide('slide', {direction: 'left'}, 400);
        }
    });
});