The simplest way to avoid an error Cannot read property 'addEventListener' of null is to check whether the variable is null or not. 

<button id="myButton">Click me</button>

 var btn = document.getElementById('myButton');
  if(btn){ //check if btn exists or not.
   btn.addEventListener('click', myFunction);
  }
 function myFunction(){
   console.log('Hello World');
 }