jQuery: auto-center an element (button) within it's parent div

auto-center-button.js

// Auto center buttons with class of js-center
// example of button HTML this would work for: <div id="sidebar-widget-stuff"><a class="btn js-center">Click Me</a></div>
(function(){
    $('.js-center').each(function(){
        var elementWidth   = $(this).outerWidth(); // measures width including padding
        var containerWidth = $(this).parent().width(); // measures width not including padding
        var marginLeftValue = containerWidth/2 - elementWidth/2;

        $(this).css('margin-left', marginLeftValue);

    });
    // grab width of each .js-center element
    // grab width of container box
    // set margin-left to 1/2 container box width - 1/2 element width
})();

Note that the above measurements consider the padding on the element. If that element's box-sizing methods change (i.e. in CSS box-sizing: content-box;) it could change which width is used here. Hope that made sense, if not just leave a comment and I'll get back to you.