className的几个方法：有无 增 删 toggle

获取元素样式类名的数组:

function getClassNames(element){
    return element.className.replace(/\s+/, ' ').split(' ');
}

检测是否存在某个样式类:

function hasClassName(element, className){
    var classes = getClassNames(element);
    for (var i=0;i<classes.length;i++){
        if(classes[i] == className){
            return true;
        }
    }
    return false;
}

添加样式类:

function addClassName(element, className){
    element.className += (element.className ? ' ':'') + className;
    return true;
}

删除样式类:

function removeClassName(element, className){
    var classes = getClassNames(element);
    var len = classes.length;
    for (var i=len-1; i>=0; i--){
        if (classes[i] == className){
            delete(classes[i]);
        }
    }
    element.className = classes.join(' ');
    return (len == classes.length ? false : true);
}

toggleClassName:

function toggleClassName(element, className){
    if (hasClassName(element, className)){
        removeClassName(element, className);
    }else{
        addClassName(element, className);
    }
}

以上方法来自高级程序设计，以前自己也写过一个类似toggleClassName的方法，

function toggleClass(element, newClass){
    var classOld = element.className;
    if (classOld.indexOf(newClass) > -1){
        element.className = classOld.replace(newClass, '')
    } else{
        element.className = classOld + " " + newClass;    
    }
}