Fits an image to window width and height whenever it changes (Part of a deprecated userscript for Mangadex)

mangadexImageFit.user.js

function CenterHandler(){
    this.$img = jQuery("#current_page");
    this.$w = jQuery(window);

    this.$w.on('resize orientationchange', this.center.bind(this));

    var MutationObserver = window.MutationObserver || window.WebKitMutationObserver || window.MozMutationObserver;

    this.observer = new MutationObserver(function(mutations) {
        mutations.forEach(function(mutation) {
            if (mutation.type === "attributes" && mutation.attributeName === "src") {
                this.center();
            }
        }.bind(this));
    }.bind(this));
    this.observer.observe(this.$img.get(0), { attributes: true });

    this.center();
    setTimeout(this.center.bind(this), 1000);
    this.applyGlobalCssChanges();
}

CenterHandler.prototype.applyGlobalCssChanges = function(){
    //jQuery("#content > .row").css("margin-bottom", 0);
    jQuery("#top_nav").css("position", "static");
    jQuery("footer.footer").css({
        "position": "static",
        "margin-top": "30px"
    });
    jQuery("body").css({
        "padding-top": 0,
        "padding-bottom": 0,
        "margin-bottom": 0
    });
};

CenterHandler.prototype.center = function() {
    var _i = this.$img.get(0),
        iw = _i.naturalWidth,
        ih = _i.naturalHeight,
        iar = iw/ih,
        ww = window.innerWidth,
        wh = window.innerHeight,
        war = ww/wh
        ;

    if (war>iar) {
        this.$img.css({
            "width": "auto",
            "height": wh+"px"
        });
    } else {
        this.$img.css({
            "width": ww+"px",
            "height": "auto"
        });
    }

    this.scroll();
};

CenterHandler.prototype.scroll = function() {
    jQuery('html, body').animate({
        scrollTop: this.$img.offset().top
    }, 300);
};





(function() {
    'use strict';

    jQuery.noConflict();
    jQuery(document).ready(function(){
        window._center = new CenterHandler();
    });

})();