Answer by Zakaria Acharki for JavaScript Changing HTML Content

Just like @j08691 mentioned in the above comment you should add quotes to getElementById() :

document.getElementById("changeString").innerHTML = "You have successfully run the report."
________________________^____________^

And to use == or === in your condition for comparison instead of equal = that used for assignment:

if (bananas === true){

And it will work as you could see below.

Hope this helps.

document.addEventListener("DOMContentLoaded", function(event) { 
  var bananas = true;

  if (bananas === true){
    document.getElementById("changeString").innerHTML = "You have successfully run the report."
  }
});

<div class="cell text-center" id="changeString"> Report has not yet been pulled for this organization.</div>