ReferenceError: document is not defined (in plain JavaScript)

Question

I get the a \"ReferenceError: document is not defined\" while trying to

var body = document.getElementsByTagName(\"body\")[0];

I have seen

Answer 1

It depends on when the self executing anonymous function is running. It is possible that it is running before window.document is defined.

In that case, try adding a listener

window.addEventListener('load', yourFunction, false);
// ..... or 
window.addEventListener('DOMContentLoaded', yourFunction, false);

yourFunction () {
  // some ocde

}

Update: (after the update of the question and inclusion of the code)

Read the following about the issues in referencing DOM elements from a JavaScript inserted and run in head element:
- “getElementsByTagName(…)[0]” is undefined?
- Traversing the DOM