“.addEventListener is not a function” why does this error occur?

The problem is with your code is that your script is executed prior to the HTML element being available. Because of the, that var comment is an empty array. So you should move your script after the html element is available. Also, getElementsByClassName returns html collection, so if you need to add event Listener to an element, you will need to do something like following

comment[0].addEventListener('click' , showComment , false ) ;
If you want to add event listener to all the elements, then you will need to loop through them
for (var i = 0 ; i < comment>

The first line of your code returns an array and assigns it to the var comment when what you want is an element assigned to the var comment...


      <code>  var comment = document.getElementsByClassName("button");</code>

So you are trying to use the method addEventListener() on the array when you need to use the method addEventListener() on the actual element within the array. You need to return an element, not an array by accessing the element within the array so the var comment itself is assigned an element not an array. Change... var comment = document.getElementsByClassName("button"); to... var comment = document.getElementsByClassName("button")[0];