Google Tag Manager Parse Error. Primary Expression

Question

I am trying to save this Custom Javascript Variable within Google Tag Manager and return this error each time:

Error at line 2, character 4: Parse error. primary expression expected

var prodID = function pID() {
return document.querySelector(".no-display > input[name=product]").value;
}();

Can someone help me? I believe I have a primary expression.

Answer 1

To fix the issue in Google tag manger, I simple re wrote the code to be :

function() {
  return document.querySelector(".no-display > input[name=product]").value;
}