How do I create a javascript variable in qualtrics that represents if a checkbox is ticked or not?

I have this code for a popup button confirming that the respondent understands the survey will be terminated if they don't agree to the consent form:

Qualtrics.SurveyEngine.addOnReady(function()
{
 /*Place your JavaScript here to run when the page is fully displayed*/
const that=this;
    this.hideNextButton();
    var btn = jQuery('<div id="Buttons"><input id="CustomButton" class="NextButton Button"  title="  Next  " type="button" name="NextButton" value=" Next  "  aria-label="Next"></div>')
    jQuery('#Buttons').append(btn);

    jQuery('#CustomButton').on('click', function(){
        var txt;
        var e= jQuery("[id='QID107']").val()
        if(e==""){
                    var r = confirm("The survey will be terminated if you do not agree with the consent form. Are you sure you wish to continue?");
                     if (r == true) {
                            that.clickNextButton();
                     } else {

                    }
        }
    });
});

I'm a novice in javascript and would like to have the variable e to refer to the choice of question QID107 which is a single checkbox for the consent form. I only want the popup with the message "The survey will be terminated (...). Are you sure you wish to continue?" to be displayed if the checkbox is left unticked and e is empty. That is what I'm trying to do with if e=="". It looks like that condition is true regardless of the answer to the consent question, so I think I'm doing something wrong but don't know what. How do I create that condition in this script? How do I correctly get the response to the consent form into e?

EDIT: The question has a condition that terminates the survey if the checkbox is left empty, so that.clickNextButton() when the checkbox is empty activates that termination condition.

Solution

Instead of checking equality for 'e' with empty string you have to check it's checked state.

jQuery("[id='QID107']").is(":checked")

This return the state of checkbox, with this you get to know that checkbox is checked or not