我怎么知道一个元素是否有一个特定的 JavaScript 类？

Question

I have a div with three button elements inside it and I want to make a JavaScript function so that if I press the first button in my div , it gets added a class called "active", and if either my second or third element had it previously, it gets removed.

 <div> <button>option 1<button/> <button>option 2<button/> <button>option 3<button/> <div>

Answer 1

var System = {
    buttonNode: {
        init: function(containerID){
            try{
                var container = e(containerID);
                var els = container.querySelectorAll(".oneActive");
                for(var i = 0; i < els.length; i++){
                    var cur = els[i];
                    cur.onclick = function(){ System.buttonNode.toggle(this); };
                }
            }catch(err){
                alert(err.stack);
            }
        },
        toggle: function(el){
            try{
                if(hasClass(el,"active")){
                    el.classList.remove("active");
                }else{
                    el.classList.add("active");
                }
            }catch(err){
                alert(err.stack);
            }
        }
    },
    e: function(id){
        return(document.getElementById(id));
    }
};
function hasClass(element, className) { //from https://stackoverflow.com/questions/5898656/check-if-an-element-contains-a-class-in-javascript
    return (' ' + element.className + ' ').indexOf(' ' + className+ ' ') > -1;
}

System.buttonNode.init("id-of-your-div-full-of-buttons");

You could probably use this.