I have attempted to toggle the button text once it's onclick here. I have use different ID for another button but it doesn't seem to work. 
How do I use the same function for multiple buttons?

```js
  function buttonToggle() {
                var change = document.getElementById("btnAdd");
                if (change.innerHTML == "ADD")
                {
                    change.innerHTML = "ADDED"
                }
                else {
                    change.innerHTML = "ADD"
                }
            }
```

```html
  <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.6/css/bootstrap.min.css" integrity="sha384-rwoIResjU2yc3z8GV/NPeZWAv56rSmLldC3R/AZzGRnGxQQKnKkoFVhFQhNUwEyJ" crossorigin="anonymous">
    <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/font-awesome.min.css">
    <link rel="stylesheet" type="text/css" href="../../css/register-dev.css"> 
    <link rel="stylesheet" href="../../css/activity-registration.css">

       <!-- jQuery first, then Tether, then Bootstrap JS. -->
    <script src="https://code.jquery.com/jquery-3.1.1.slim.min.js" integrity="sha384-A7FZj7v+d/sdmMqp/nOQwliLvUsJfDHW+k9Omg/a/EheAdgtzNs3hpfag6Ed950n" crossorigin="anonymous"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/tether/1.4.0/js/tether.min.js" integrity="sha384-DztdAPBWPRXSA/3eYEEUWrWCy7G5KFbe8fFjk5JAIxUYHKkDx6Qin1DkWx51bBrb" crossorigin="anonymous"></script>
    <script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.6/js/bootstrap.min.js" integrity="sha384-vBWWzlZJ8ea9aCX4pEW3rVHjgjt7zpkNpZk+02D9phzyeVkE+jo0ieGizqPLForn" crossorigin="anonymous"></script>
    <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>

  <div class="col">
      <button type="button" class="btn btn-primary btn-lg" id="btnAdd" onclick="buttonToggle()">
     <span><i class="fa fa-plus" aria-hidden="true"></i> <b>ADD</b></span>
       </button>
        </div>

<br>
<br>

<div class="col">
   <button type="button" class="btn btn-primary btn-lg" id="btnAdd3" onclick="buttonToggle()">
       <span><i class="fa fa-plus" aria-hidden="true"></i></span> <b>ADD</b>
    </button>
       </div>
```