操作类名

原生

node.classList.remove(someClass);
node.classList.add(newClass);
node.classList.contains(someClass);

模拟

function addClass(node, newClass) {
    var arr = node.className.split(/\s+/);
    arr.push(newClass);
    return arr.join(' ');
}

function removeClass(node, someClass) {
    var arr = node.className.split(/\s+/);
    arr = arr.filter(item => {
        item !== someClass;
    })
    return arr.join(' ');
}

function containClass(node, someClass) {
    var arr = node.className.split(/\s+/);
    return arr.forEach(item => {
        if (item === someClass) {
            return true;
        }
    })
}