Pass custom value to in built xApi statements

Hi Phil,

Yes, I am currently using the 'Execute JavaScript' trigger to get value from URL.

// Function to get parameter from URL
function getParameterByName(name, url) {
    if (!url) url = window.location.href;
    name = name.replace(/[\[\]]/g, "\\$&");
    var regex = new RegExp("[?&]" + name + "(=([^&#]*)|&|#|$)"),
        results = regex.exec(url);
    if (!results) return null;
    if (!results[2]) return '';
    return decodeURIComponent(results[2].replace(/\+/g, " "));
}

// Retrieve courseId parameter from the URL
var courseId = getParameterByName('courseId');

// Set the courseId value to a Storyline variable
var player = GetPlayer();

player.SetVar("CourseID", courseId);

var courseIDFromVariable = player.GetVar("CourseID");

alert("Course ID: " + courseId);
alert("Course ID from variable: " + courseIDFromVariable);

Using the above code, I was able to successfully capture the courseId from the URL. However, I encountered another issue when trying to set the articulate variable, which is that it is always returning null, even when I use a hardcoded value like this.
player.SetVar("CourseID", 15);
player.GetVar("CourseID"); this always returned a null value.

This is where I am currently stuck. I don't even know if this is the right way. I would like to know if I am able to fix the setting variable, Can I only set this value to custom xApi statements, not to the in-built xApi statements? Sorry for any confusion; I am very new to the articulate. Any help would be much appreciated.