activeElement解决ios滚动到底部显示内容时，键盘挡住显示内容的问题

        let header = document.getElementById(‘header‘);
        let footerfreeclass = document.getElementById(‘FooterFreeClass‘);

        let wholeScrollHeight = document.documentElement.scrollHeight, // 能滚动的总高度
            visiableHeight = document.documentElement.clientHeight, // 可视区域高度
            currentOffset = document.documentElement.scrollTop || document.body.scrollTop; // 滚动的距离
        if (currentOffset > 200) {
            header.classList.add(‘nav-header-change‘);
        } else {
            header.classList.remove(‘nav-header-change‘);
        }
        if (footerfreeclass !== undefined && footerfreeclass !== null) {
            if (currentOffset > 200 && wholeScrollHeight - currentOffset - visiableHeight > 400) {
                footerfreeclass.classList.add(‘footer-freeclass-block‘);
            } else {
                let currentFocusEle = document.activeElement;
                if (currentFocusEle.className === "header-freeclass-input footer-freeclass-input") {
                    //解决键盘弹出导致其隐藏的bug
                    return false;
                }
                footerfreeclass.classList.remove(‘footer-freeclass-block‘);
            }   
        }