JS + changing element CSS + named anchors

I need help with some javascript, cos I'm a total newbie at it.

Basically the effect I'm working on is to have a nice landing page, with several links, and when the links are clicked, that whole initial "screen" should slide to the side and become a side-menu bar.

I got that far. I achieved it by using these tips: Change an element's CSS class with JavaScript

Basically I change the div layers' CSS class with onclick js actions and get a nice sliding effect with css transitions.

However, that's not enough. The problem is that there is no way to give someone a direct link to one of the pseudo "sub-pages" then. Every time the page is loaded, it shows the landing screen again. I could use named anchors maybe, to "activate" a specific div layer.

But I don't know how to do that. I would have to execute a specific javascript function depending on the URL from which the page is being accessed... and umm... that's over my head.

Maybe I'm setting everything up completely wrong to begin with? I don't know... I hope someone can help. :(

Here's my jsfiddle:

http://ift.tt/1E7yNRN

html:

<div id="overlay">
OVERLAY (menu)
<br /><br />
<a href="#one" id="link">link</a><br />
<a href="#two" id="linktwo">link2</a>
</div>

<div id="div1">
<a name="one" id="one"></a>
THIS IS LINK ONE DIV
</div>

<div id="div2">
<a name="two" id="two"></a>
THIS IS LINK TWO DIV
</div>

CSS:

body,html{
    margin: 0;
    padding: 0;
    background:#fff;
    color: #000;
}

#div1,
#div2{
    visibility: hidden;
    opacity: 0;
    -webkit-transition: opacity 1s linear; 
    transition: opacity 1s linear;
    -moz-transition: opacity 1s linear;
    -o-transition: opacity 1s linear;
}

.visible{
    float: left;
    width: 65%;
    border: 1px solid #369;
    visibility: visible!important;
    filter:alpha(opacity=100)!important; /* For IE8 and earlier */
    opacity: 1!important;
    -webkit-transition: opacity 2s linear; 
    transition: opacity 2s linear;
    -moz-transition: opacity 2s linear;
    -o-transition: opacity 2s linear;
}

#overlay{
    height: 100%;
    width: 100%;
    position: absolute;
    top: 0;
    right: 0;
    background: #999;
    color: #fff;
    text-align: center;
    -webkit-transition: all 0.4s ease-in-out; 
    transition: all 0.4s ease-in-out;
    -moz-transition: all 0.4s ease-in-out;
    -o-transition: all 0.4s ease-in-out;

}

.menu{
    width: 35%!important;
    position: fixed!important;
    top: 0;
    right: 0;
    background-color:#b9bcab;
    height: 100%;
    -webkit-transition: all 0.7s ease-in-out; 
    transition: all 0.7s ease-in-out;
    -moz-transition: all 0.7s ease-in-out;
    -o-transition: all 0.7s ease-in-out;

}

and the JS:

function visibleone()
    {
        document.getElementById("overlay").className = "menu";
        document.getElementById("div1").className = "visible";
        document.getElementById("div2").className =
        document.getElementById("div2").className.replace
      ( /(?:^|\s)visible(?!\S)/g , '' )
    }

function visibletwo()
    {
        document.getElementById("overlay").className = "menu";
        document.getElementById("div2").className = "visible";
        document.getElementById("div1").className =
        document.getElementById("div1").className.replace
      ( /(?:^|\s)visible(?!\S)/g , '' )

    }


 window.onload = function()
    {
    document.getElementById("link").addEventListener( 'click' , visibleone );
    document.getElementById("linktwo").addEventListener( 'click' , visibletwo );
    }