添加类名，移除类名，正则表达式实现

var reg = new RegExp("(?:^|\\s+)" + target_class + "(?=\\s+|$)");

function addClass(el, clas){
    var reg = new RegExp("(^|\\s)" + clas + "(\\s|$)"),
        trim = /^\s+|\s+$/g,
        classStr = el.className;

    classStr = classStr.replace(trim, ""); // 先删除类名前后的空格
    el.className = reg.test(classStr) ? classStr : classStr ? classStr + " " + clas : clas;
}

function removeClass(el, clas){
    var reg = new RegExp("(?:^|\\s+)" + clas + "(?=\\s+|$)", "g"),
        trim = /^\s+|\s+$/g,
        classStr = el.className;

    classStr = classStr.replace(reg, "");
    el.className = classStr.replace(trim, ""); //最后删除类名前后空格
}