Computing the total width of all children elements inside of a given parent

Adding up element's widths

//with jQuery
var parent = $(selector)
    , totalWidthOfChildren = Array.prototype.reduce.call(parent.children(), function(a,b){ return a + $(b).outerWidth( true ); }, 0);
    
//without jquery
var parent = document.getElementById('selector')
    , totalWidthOfChildren = Array.prototype.reduce.call(parent.children, function(a,b){ return a + outerWidth(b); }, 0);
    
function outerWidth( elem ) {

    var styles;
    
    if( window.getComputedStyle ) {
    
        var parts = ["width", "paddingLeft", "paddingRight", "marginLeft", "marginRight"];
        
        styles = window.getComputedStyle( elem );
        
        return parts.reduce(function(a,b) {
            return a + +styles[b].replace(/px/, '');
        }, 0);
    }
}