Custom conditional in Google Sheets: How to integrate in Apps Script?

My goal is to have Google Sheets detect when a cell's contents has a strikethrough added, and to change the font color of that cell in response. I learned that this is not possible without an Apps Script integration.

First, I needed a function that identifies whether a cell has strikethrough text. I found this code on Stack Exchange, and it works as a formula when used in a sheet:

function has_strikethrough(reference) {  var sheet = SpreadsheetApp.getActiveSheet();  var formula = SpreadsheetApp.getActiveRange().getFormula();  var fParts=formula.split(')').shift()  var rang=fParts.split('(').pop()  try {    var range = sheet.getRange(rang);  }  catch(e) {    throw new Error(args[1] +' is not a valid range');  }  var lines = range.getFontLines(); // return lines.length;  var output = [];  for (var i = 0; i < lines.length; i++) {    output.push(lines[i].map(function(a) {return a == 'line-through';}));  }  return output;}

It allows me to derive a boolean result if I use this formula:

=has_strikethrough(A1)=TRUE

This cannot be integrated into a conditional rule within Google Sheets, however, and for that, I learned that I need to create a conditional directly in Apps Script. I found some simple default code that is supposed to do this, but I don't seem to know how to integrate my strikethrough function into it properly. When I add the following code, and include the "whenFormulaSatisfied" boolean, the function breaks and the conditional does not work:

var sheet = SpreadsheetApp.getActiveSheet();var range = sheet.getRange("C3:D");var rule = SpreadsheetApp.newConditionalFormatRule()    .whenFormulaSatisfied("=has_strikethrough(C3)=TRUE")    .setFontColor("#666")    .setRanges([range])    .build();var rules = sheet.getConditionalFormatRules();rules.push(rule);sheet.setConditionalFormatRules(rules);

Running in the console gives this error:

ReferenceError: args is not defined

Is there a simple step I'm missing? Any help would be appreciated. Thanks!