StickyBar (js) es6 + babel + jQuery

code.js

/**
 * ENG
 * Makes element fixed only for the mobile version of site (until 768px)
 * @constructor
 * @param {string} sTarget - target css-class for the element, which becomes fixed (.j-sticky-bar)
 * @param {string} sFixedClass - the name of the css-class you want to add to the sTarget element (j-fixed)
 * @param {sContent} sFixedClass - when sTarget becomes fixed, sContent element gets additional padding-top (body)
 */

/**
 * RUS
 * Делает элемент фиксированным (только для моб. версии сайта до 768px)
 * @constructor
 * @param {string} sTarget - css-класс для элемента, который становится фиксированным (.j-sticky-bar)
 * @param {string} sFixedClass - css-класс, который добавится sTarget-элементу (j-fixed)
 * @param {sContent} sFixedClass - когда sTarget получает sFixedClass sContent получает дополнительный отступ (body)
 */
export default class stickyBar {
    constructor(sTarget = ".j-sticky-bar", sFixedClass = "j-fixed", sContent = 'body') {
        this._oTarget = ($(sTarget).get(0));
        this._oContent = ($(sContent).get(0));
        this._iTargetTop = null;
        this._iTargetHeight = null;
        this._iStartPoint = null;
        this._iWindowPoint = null;

        this._getStartedParams = () => {
            this._iTargetTop = this._oTarget.offsetTop;
            this._iTargetHeight = this._oTarget.offsetHeight;
            this._iStartPoint = this._iTargetTop + (this._iTargetHeight * 2);
        };

        this._getWindowPoint = () => {
            this._iWindowPoint = window.pageYOffset;
        };

        this.fixedOn = () => {
            $(this._oTarget).addClass(sFixedClass);
            $(this._oContent).css("padding-top", this._iTargetHeight + "px" );
        };

        this.fixedOff = () => {
            $(this._oTarget).removeClass(sFixedClass);
            $(this._oContent).css("padding-top", "initial" );
        };

        this.checkState = () => {
            if ((this._iStartPoint <= this._iWindowPoint) && (window.innerWidth < 768)) {
                this.fixedOn();
            } else {
                this.fixedOff();
            }
        };

        this.afterResize = () => {
            if ($(this._oTarget).height() > 0) {
                this._getStartedParams();
                this._getWindowPoint();
                this.checkState();
            } else {
                this.fixedOff();
            }
        };

        $(window).on("load", ()=> {
            this._getStartedParams();
        });

        $(window).on("scroll", ()=> {
            this._getWindowPoint();
            this.checkState();
        });

        $(window).on("resize", ()=> {
            this.afterResize();
        });
    }
}