Comment extraire tous les styles appliqués à un élément à l'aide de son identifiant en JavaScript ?

function getStyleById(id) {
    return getAllStyles(document.getElementById(id));
}
function getAllStyles(elem) {
    // Check if element exists (empty list if not)
    if (!elem) return [];

    var win = document.defaultView || window, style, styleNode = [];

    // Modern browsers
    if (win.getComputedStyle) {
        style = win.getComputedStyle(elem, '');

        // Loop through style properties and gather values
        for (var i = 0; i < style.length; i++) {
            styleNode.push( style[i] + ':' + style.getPropertyValue(style[i]) );
        }
    } 
    // IE
    else if (elem.currentStyle) {
        style = elem.currentStyle;

        // Loop through currentStyle properties
        for (var name in style) {
            styleNode.push( name + ':' + style[name] );
        }
    } 
    // Ancient browsers
    else {
        style = elem.style;

        // Loop through inline styles
        for (var i = 0; i < style.length; i++) {
            styleNode.push( style[i] + ':' + style[style[i]] );
        }
    }

    // Return list of style properties
    return styleNode;
}