画面サイズが640px以下になればメニューを折りたたみます。

スマホ時は、横からメニューがスライドインします。

JSを読み込みます

<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.2/jquery.min.js"></script>
<script src="https://codingmania.net/demo/form/0014/js/main.js"></script>

[main.js]JavaScript

$(function(){

//メニュー
//SET
if($(".Header__btn").css("display") == "block") {
    windowWidth = $(window).width();
    $(".Globalnav").css({"margin-left":windowWidth, "width":windowWidth,"display":"block"});
}
//risize
var setwidth = $(window).width();
var timer = false;
$(window).resize(function() {
    if (timer !== false) {
        clearTimeout(timer);
    }
    timer = setTimeout(function() {
    var ww = $(window).width();
    windowWidth = $(window).width();
    if(windowWidth == setwidth){
    }else if(windowWidth<640){
    $(".Header__btn p").addClass("close").removeClass("open");
    $(".Header__btn p img").attr("src","common/img/icon_menu.png");
    $(".Globalnav").css({"margin-left":windowWidth, "width":windowWidth,"display":"block"});
    }else{
    $(".Globalnav").css({"margin":"0 auto", "width":950});
    };
    }, 50);
});

//orientationchange
$(function(){
var timer = false;
    //$(window).on("orientationchange", function() {
    $(window).on("orientationchange", function() {
    if(timer !== false){
        clearTimeout(timer);
    }
    timer = setTimeout(function() {
    //window.onorientationchange = function(){
    windowWidth = $(window).width();
    //alert(windowWidth);
    if(windowWidth<640){
    $(".Header__btn p").addClass("close").removeClass("open");
    $(".Header__btn p img").attr("src","common/img/icon_menu.png");
    $(".Globalnav").css({"margin-left":windowWidth, "width":windowWidth,"display":"block"});
    }else{
    $(".Globalnav").css({"margin":"0 auto", "width":950});
    }
    }, 1);
    });
});

//click
  $(".Header__btn p").click(function() {
if($(this).hasClass("open")) {
    $(this).addClass("close").removeClass("open");
    //var windowWidth = $(window).width();
    $(".Header__btn p img").attr("src","common/img/icon_menu.png");
    $(".Globalnav").animate({"marginLeft":windowWidth+"px"},500);
    //alert(windowWidth);
} else {
    $(this).addClass("open").removeClass("close");
    $(".Header__btn p img").attr("src","common/img/icon_menu-close.png");
    $(".Globalnav").animate({"marginLeft":"0px"},500);
}

});

});

HTMl

<header class="Header" role="banner">
<div class="Header__btn">
<p><a href="javascript:void(0)"><span>メニューを開く</span></a></p>
<!-- /.Header__btn --></div>
<nav class="Globalnav" role="navigation" aria-label="メインメニュー">
<ul>
<li class="current"><a href="#">TOPページ</a></li>
<li><a href="#">メニューその1</a></li>
<li><a href="#">メニューその2</a></li>
<li><a href="#">メニューその3</a></li>
<li><a href="#">メニューその4</a></li>
<li><a href="#">メニューその5</a></li>
</ul>
<!-- /.Globalnav --></nav>
<!-- /.Header --></header>

CSS

/* Header
-----------------------------------------*/
@media screen and (max-width: 640px) {
.Header{
  position: relative;
  height: 50px;
}
}
.Header__btn{
  display: none;
}
@media screen and (max-width: 640px) {
.Header__btn{
  position: absolute;
  top:0px;
  right: 0px;
  display: block;
  background-color: #489fdf;
}
.Header__btn p a{
  display: block;
    width: 50px;
    height: 50px;
}
  .Header__btn p a:after {
    position: absolute;
    display: block;
    content: " \f0c9";
    font-family: FontAwesome;
    width: 50px;
    height: 50px;
    top: 14px;
    left:0;
    right: 0;
    font-size: 22px;
    color: #FFF;
    text-align: center;
  }
  .Header__btn p.open a:after {
    content: " \f00d";
  }
.Header__btn span{
  display: block;
  width: 1px;
  height: 1px;
  overflow: hidden;
}

}
/* Globalnav
-----------------------------------------*/
@media screen and (max-width: 640px) {
  body {
    overflow: hidden;
  }
}
.Globalnav {
  margin: 0 auto;
  width: 950px;
}

@media screen and (max-width: 640px) {
  .Globalnav {
    width: auto;
  }
}

@media screen and (max-width: 640px) {
  .Globalnav {
    display: none;
    position: absolute;
    top: 50px;
    left: 0;
    margin-left: 320px;
    width: 320px;
    z-index: 9999;
    background-color: #489fdf;
  }
}

.Globalnav ul {
  display: table;
  width: 100%;
}

@media screen and (max-width: 640px) {
  .Globalnav ul {
    display:block;
    width: 100%;
    box-sizing: border-box;
    padding: 15px 10px;
  }
}

.Globalnav ul li {
  display: table-cell;
}
@media screen and (max-width: 640px) {
  .Globalnav ul li {
   display: block;
    margin: 0;
    border-bottom: solid 1px #FFF;
  }
  .Globalnav ul li:last-child{
    border-bottom: none;
  }
}

.Globalnav ul li a {
  display: block;
  text-align: center;
  padding: 20px 0;
  color: #000;
  font-size: 16px;
  font-weight: bold;
  text-decoration: none;
  border-bottom: solid 3px #FFF;
}

@media screen and (max-width: 640px) {
  .Globalnav ul li a {
    position: relative;
    padding: 15px 0;
    font-size: 14px;
    border: none;
    color: #FFF;
    text-align: left;
  }
}

@media screen and (max-width: 640px) {
  .Globalnav ul li a:after {
    position: absolute;
    content: " \f105";
    font-family: FontAwesome;
    width: 20px;
    height: 7px;
    top: 50%;
    margin-top: -10px;
    right: 0;
  }
}

.Globalnav ul li a:hover, .Globalnav ul li a:focus, .Globalnav ul li.current a {
  border-bottom: solid 3px #489fdf;
  color: #489fdf;
}

@media screen and (max-width: 640px) {
  .Globalnav ul li a:hover, .Globalnav ul li a:focus, .Globalnav ul li.current a {
    border-bottom: none;
    color: #FFF;
  }
}