Why is the window.width smaller than the viewport

Question

I am quite puzzled and still unsure how to explain this in proper words. So far i've used and set up my media queries with Breakpoint. An used Breakpoint-variable looks like e.g.:

$menustatictofixed: min-width 900px;

$breakpoint-to-ems is set to true. I've laid out the page with all its Breakpoint variables based on the pixel values of the following jQuery snippet:

$('body').append('<div style="position: fixed; bottom: 0; right: 0; display: inline-block; font-weight: bold; padding: 5px 7px; border-radius: 5px 0 0 0; background: green; color: white; z-index: 9999;">Viewport width <span id="width"></span> px</div>');
var viewportWidth = $(window).width()
$('#width').text(viewportWidth);
$(window).resize(function() {
  var viewportWidth = $(window).width();
    $('#width').text(viewportWidth);
});

Everything looked proper and clean. But over the last one or two days i had issues setting up the last breakpoints for a pattern and to get things behave predictable. Somehow the things that appeared to add up clean and fine in the first place, which i logically highly doubt now, are in fact improper and somehow a mess. Cuz if you take a look at the following screenshot somehow the width of the window (in Chrome) differs to the width from the jQuery snippet utilising window.width. There isn't also a difference if i would replace window.width by window.innerWidth to rule out scrollbars eventually. The only way to receive proper results is by adding 15 pixels to the equation:

var viewportWidth = $(window).width() + 15;

Is the only issue in the whole equation that window.width is the wrong choice of function and it would be better to go with e.g. document.documentElement.clientWidth or something else or ... ? And for what the 15 pixels are standing for which fixed the problem above in a bit hacky way? Best regards Ralf

Answer 1

Similar to @Snugugs's answer but worked better for my use case:

CSS (Note I am using LESS so @tabletMin and @desktopMin translate to breakpoint variables I have set elsewhere:

    #cssWidth {
        display:none;
        content:'mobile';
    }

    /* Responsive styles (Tablet) */
    @media (min-width: @tabletMin) {
        #cssWidth {
            content:'tablet';
        }
        /* Other tablet CSS... */
    }
    /* Responsive styles (Desktop) */
    @media (min-width: @desktopMin) {
        #cssWidth {
            content:'desktop';
        }
        /* Other Desktop CSS... */
    }

And then in JS:

    getView = function() {
        // If #cssWidth element does not exist, create it and prepend it do body
        if ($('#cssWidth').length === 0) {
            $('body').prepend($(document.createElement('div')).attr('id', 'cssWidth'));
        }
        // Return the value of the elements 'content' property
        return $('#cssWidth').css('content');
    };

The getView() function will then return the string 'mobile', 'tablet' or 'desktop' dependant on the width the media queries see.

This could be extended to fit more viewport widths, just add more rules in the CSS with other values.