Invoke Js function to set Composite Component attribute

Question

I have a composite component, and for setting one of it's attributes I have to call a Js function that makes a calculation. How can I do this?

JS Function

function getContWidth() {
             var width = ($("#content_container_wide").css("width"));
             return width;
        };

Comp Component

<comp:carouselComponent id="carousel" title="Carousel images" 
                        images="#{carouselBean.imageList}"
                        height="170" numToDisplay="3" 
                        width="#{document.write(getContWidth())}" />