Keep Aspect Ratio (new oop version)

keepratio.js

// Keeps aspect ratio of an element by listening to window resize event
// and setting height = width / aspect ratio
//
// Copyright (c) 2015 Aleksandr Efremov
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
//
// Compress with GCC --compilation_level ADVANCED_OPTIMIZATIONS
// Usage: var myKeeper = new Keeper();
// myKeeper.keep(ID, ratio); // Start keeper
// myKeeper.keep(); // Without any parameters - stop keeper and restore the initial height value
//
// I'm using underscores before property names, to make GCC to compress them
(function () {
    // Using this as a namespace proxy
    this['Keeper'] = Keeper;

    function Keeper () {}

    Keeper.prototype['keep'] = function (ID, ratio) {
        // Stops previous listener if exists
        window.removeEventListener('resize', this._handler, false);

        // If started first time, there is no initial value
        if (this._element) {
            // If there is initial value, then it was already started with the ratio argument
            this._element.style.height = this._initValue;
            // Do it only once
            this._element = null;
        }

        var element = document.getElementById(ID);

        if (ratio && element) {
            this._ratio = ratio;
            this._element = element;

            // Save the height value, to be able to restore it later
            this._initValue = element.style.height;

            // Trick to avoide closures
            this._handler = this._origHandler.bind(this);

            window.addEventListener('resize', this._handler);
            // The callback will fire on resize, but we want it the first time to fire immediately
            this._handler();
        }
    };

    Keeper.prototype._origHandler = function () {
        this._element.style.height = (parseFloat(getComputedStyle(this._element, null).width) / this._ratio) + 'px';
    };
})();