JavaScript: Event listener for multiple buttons with same class name

What you are really looking for is JavaScript Event Delegation. In your case, you have BUTTON elements, which I'm going to assume are <button> tags. Now you want to know when one of those buttons was clicked and then run a function:

if (document.addEventListener) {
    document.addEventListener("click", handleClick, false);
}
else if (document.attachEvent) {
    document.attachEvent("onclick", handleClick);
}

function handleClick(event) {
    event = event || window.event;
    event.target = event.target || event.srcElement;

    var element = event.target;

    // Climb up the document tree from the target of the event
    while (element) {
        if (element.nodeName === "BUTTON" && /foo/.test(element.className)) {
            // The user clicked on a <button> or clicked on an element inside a <button>
            // with a class name called "foo"
            doSomething(element);
            break;
        }

        element = element.parentNode;
    }
}

function doSomething(button) {
    // do something with button
}

Anywhere on the page that a <button class="foo">...</button> element appears, clicking it, or any HTML tag inside of it, will run the doSomething function.

Update: Since Event Delegation is used, only a single click handler is registered on the document object. If more <button>s are created as a result of an AJAX call, you don't have to register click handlers on those new <button>s since we take advantage of the click event bubbling up from the element the user clicked on to the document object itself.

If you don't have jquery:

if (document.body.addEventListener){
    document.body.addEventListener('click',yourHandler,false);
}
else{
    document.body.attachEvent('onclick',yourHandler);//for IE
}

function yourHandler(e){
    e = e || window.event;
    var target = e.target || e.srcElement;
    if (target.className.match(/keyword/))
    {
        //an element with the keyword Class was clicked
    }
}

If you use a cross browser library like jquery:

HTML:

<div class="myClass">sample</div>
<div class="myClass">sample 2</div>

JS:

function theFuncToCall(event){
  //func code
}

$(document).on('click', '.myClass', theFuncToCall);