How can I skew one side of a div and then replicate it and skew a different side?

Question

Suppose I have a div:

div {
    height: 100px; 
    width: 500px; 
    background: blue; 
    margin: 0 auto; 
} 

And I want it to become two mode - skew to each side -

Here is the base form - http://jsfiddle.net/urielz/neybabgj/

How could I get the above two forms?

Update :

If it required using JavaScript - do it.

Answer 1

JSiddle Demo

CSS

div {
    height : 100px;
    width : 500px;
    background : blue;
    margin : 10px auto;
    position: relative;
}
div:first-child:before {
    position: absolute;
    top:0;
    right:100%;
    width:0;
    height:0;
    content:'';
    border:50px solid blue;
    border-top-color:transparent;
    border-left-color:transparent;
}

div:nth-child(2):after {
    position: absolute;
    top:0;
    left:100%;
    width:0;
    height:0;
    content:'';
    border:50px solid blue;
    border-bottom-color:transparent;
    border-right-color:transparent;
}

Answer 2

HTML

<div class="crop">
    <div class="skew"></div>
</div>

CSS

.crop {
    width: 492px;
    height: 240px;
    overflow: hidden;
}
.skew {
    display: block;
    height : 100px;
    width : 500px;
    background : blue;
    margin : 0 auto 0 32px;
    position:relative;
    -webkit-transform: skew(-30deg);
    -moz-transform: skew(-30deg);
    -ms-transform: skew(-30deg);
    transform: skew(-30deg);
}
.skew:after {
    height : 100px;
    width : 500px;
    background : blue;
    margin : 0 auto;
    position:absolute;
    bottom: -120px;
    content:'';
}

Fiddle: http://jsfiddle.net/neybabgj/7/