无法读取 null 的属性“addEventListener”（JavaScript Sails App）

Question

I am trying the below JavaScript code of onsip in sails app to apply video call, but it gives the error:

Cannot read property addEventListener' of null

Below is the JavaScript code for it:

button.addEventListener('click', function() {
  // Was on a call, so the button press means we are hanging up
  if (onCall) {
    onCall = false;
    button.firstChild.nodeValue = 'video';
    remoteRender.style.visibility = 'hidden';
    session.bye();
    session = null;
  }
  // Was not on a call, so the button press means we are ringing someone
  else {
    onCall = true;
    button.firstChild.nodeValue = 'hang up';
    remoteRender.style.visibility = 'visible';
    session = makeCall(userAgent, target,
      false, true,
      remoteRender, null);
    session.on('bye', function() {
      onCall = false;
      button.firstChild.nodeValue = 'video';
      remoteRender.style.visibility = 'hidden';
      session = null;
    });
  }
});

HTML code for the above is:

<button id="alice-video-button" class="right" type="button">video</button>

Answer 1

As i know about this error : " Cannot read property 'addEventListener' of null"

if you get this error any where in your code, you need to check about id's and selectors.

button.addEventListener('click', function () {..}

Probably you get your error on this line and check this "button" variable is set.

Hope this will help