Howdy. I had the same problem. I solved it by putting the function and its variables into a string, writing it to file, then calling the file using the Javascript in browser. Works a treat. Like this;

@BeauG107806 Thanks for the approach. I am using this way to write this snippet in the file and then call it 
function getFieldValue () {var field = document.querySelector("#id");return field.value;}

Now it is completing without any error but the output returned is also an empty value.
Same snippet I use it in the console of the browser it gives the desired output. 

Any specific form of encoding that I need to save the file, in the log to file command?