I am using AJAX to load a list of comic chapters on click. It works fine. I would like to modify the script to hide the chapters when I click again on the same book. Hopefully the below pictures will make it clear.

The code to load the chapters is as follows:

function aload(element) {
    var url = element.getAttribute('data-ajax-url');
    var xhr = new XMLHttpRequest();
    xhr.open("POST", url);
    xhr.setRequestHeader("X-CSRFToken", csrftoken);
    xhr.onreadystatechange = function() {
        if (xhr.readyState === 4){
            document.getElementById("chapter-container").innerHTML = this.response;
        }
    }
    xhr.send();
}

Thank you for all your suggestions.