Import external JS library not working?

Yes. Qualtrics will block them. Use jQuery.getScript() to get around this.
jQuery.getScript("URL", function(){.....code here...});

Hi ahmedA , thanks for your help!

I changed the code as follows, and it is not working:
Qualtrics.SurveyEngine.addOnload(function()
{
jQuery.getScript("https://raw.githubusercontent.com/arhs/iban.js/master/iban.js", function(){
window.timerID = setInterval('var check = IBAN.isValid(document.getElementById("QR~QID38~7").value);console.log(check)',200);
});


/* Change input method to Enter, with input validation */
document.on("keydown", function(e) {
if (e.keyCode === 13 && check == true) $('NextButton').click();
})

document.on("keydown", function(e) {
if (e.keyCode === 13 && check == false)
{
alert("Bitte geben Sie eine gültige IBAN ein.") ;
}
})


});
What am I doing wrong?

Also, my previous solution (calling the library from the header and then using the function in the question) was working until a few days ago and it is also reported in Qualtrics Javascript Guidelines (https://www.qualtrics.com/support/survey-platform/survey-module/question-options/add-javascript/): do you have any idea of why this is not working anymore?

Thanks again!

Since its hosted on Github, its not a problem with Qualtrics but instead with Github not allows CORS. Use githack and use that URL.
However, I would recommend you revise your code, since its using too many resources needlessly.

Hi ahmedA , thanks for your suggestion and sorry for the late reply!
The issue is not Github per se, as originally I used Qualtrics itself as a host. Potentially also Qualtrics does not allow CORS. If that's the case, there's a need for a general fix IMHO, as this method is currently the only way to use external libraries.

CORS stands for cross origin. If you have it in your library, then there should be no problem with CORS, because the origin and the destination will correspond to the same domain.