Global scope for Javascript variables in Storyline

(2nd try to post, don't know why 1st disappeared)

Hi everyone, 

One year later and I'm asked to build a tool that helps tracking user progress, but not through how many slides have been seen/accessed as Storyline allows it, but through how many buttons have been clicked (inside a list of which buttons to track) inside several slides.
This tool (set of scripts) will be used by co-workers who have no skill at all in coding, si I try to make it as easy as possible to use.
I first made an Excel sheet that contains a table they have to fill. The table goes like this :

slide1name | slide2name  | etc.
button1A   | button2A    | etc.
button1B   | button2B    | etc.
           | button2C    |

first line contains the slide names we want to track (not storyline names or references,  but decided by my co-worker)
Then for each slide name, the column below contains the names of the buttons whose click we want to track (once again, those names are not from storyline but decided by my co-worker).

Then I use in excel formulas to create the javascript line that declares a multidimensionnal array : 
[[list of slide names],[[[list of button names of 1st slide],[list of their states]],[ (same for slide 2) ],[etc.]]]

for example, with 3 slides named "sliA", "sliB" and "sliC" ; sliA containing 2 buttons to track, sliB 3 buttons and sliC 4 buttons, the js declaration of the array is 

let tabProgress=[['sliA','sliB','sliC'],[[['butA1','butA2'],[0,0]],[['butB1','butB2','butB3'],[0,0,0]],[['butC1','butC2','butC3','butC4'],[0,0,0,0]]]];

my idea is to call javascript functions I place in a js file loaded thank's to Math's globalScript solution :

• to get or set the state for any given button in any given slide :
  • I search for the slide name in first sub-array, get it's position
  • I search for the sub-sub array in 2nd sub-array at the same position
  • I search for the button name if the first array of the sub-sub array, and get or set the value in the 2nd one at the same position.
• to calculate the percentage of buttons clicked for a given slide,
• to calculate the percentage of buttons clicked for all slides.

I added a single "getGlobalValue" function to Math's globalScript.js, just to get my array before passing it to the above functions.
Here's the modified globaScript.js file :

console.log("globalScripts.js loaded");
/*
globObj is a global Object to save data too
*/

const globObj = {};
// we could use multiple objects and pass/read data
const semiGlobObj = {};

/*
Global functions that can be called from anywhere in Storyline.
Any needed functions can be added here and you can call them directly in Storyline.
*/

/*
This function creates properties on any given object that then can be reused anywhere.
Eval is needed to get the proper Object and bracket notation [] is needed to convert
the input to a literal name for the property
*/
function setGlobalValue(_val,_prop,_obj){
        console.log("set: "+_obj+" | "+_prop);
            let obj2Use = eval(_obj);
                Object.defineProperties(obj2Use, {
                  [_prop]: {
                    value: _val,
                    writable: true
                  }
                });
        console.log("set: "+_obj+" | "+_prop+" = "+obj2Use[_prop]);
}

/* added by E.Nédélec
*/
function getGlobalValue(_prop,_obj) {
	console.log("get: "+_obj+" | "+_prop);
    obj2Use = eval(_obj);
    console.log ("return : " + obj2Use[_prop].value);
	return obj2Use[_prop].value;
} 

/*
    Function to loop and iterate an Object in Storyline.
    Returns a string or an array depending on chosen _desiredoutput
*/

function iterateObject(_obj,_desiredoutput){
    const propsArr = Object.getOwnPropertyNames(_obj);
    let valuesArr = [];
    console.log(propsArr);
    let str = "";
   for(var i = 0; i < propsArr.length; i++){
      let prop = propsArr[i];
      console.log("prop: "+prop);
      let val = globObj[prop];
      valuesArr.push(globObj[prop]);
      console.log("val: "+val);
      str += propsArr[i]+" "+val+"\n";
     }
     if(_desiredoutput=="array"){
        return propsArr
     }else{
        return str;
     }
}

When I run my projet, here's what appears in the browser's console : 

globalScripts.js loaded globalScripts.js:1:9
1 JS / story_content/WebObjects/6Tdp61PnyWP/globals/globalScripts.js loaded. user.js:28:15
jsProgess.js loaded jsProgress.js:1:9
2 JS / story_content/WebObjects/6Tdp61PnyWP/globals/jsProgress.js loaded. user.js:28:15
set: globObj | tabProgress globalScripts.js:21:17
set: globObj | tabProgress = sliA,sliB,sliC,butA1,butA2,0,0,butB1,butB2,butB3,0,0,0,butC1,butC2,butC3,butC4,0,0,0,0 globalScripts.js:29:17
get: globObj | tabProgress globalScripts.js:35:10
return : undefined

So my array seems properly set in the global object, my "getGlobalValue" function seems properly called, but why does it return "undefined" ?
This is driving me nuts 😣