The code should show the plot for the book cover you click on whilst changing the background to an alternative cover of the book, but it isn't doing anything. I have some backup code that works, but I liked this solution more.

My js code:

function mostraTrama(){
    try{
        switch(this.id){
            case "TramaVdR":
                nodoTramaVdR.setAttribute = ("class", "TramaScelta");
                nodoTramaPdL.setAttribute = ("class", "TramaNonScelta");
                nodoTramaG.setAttribute = ("class", "TramaNonScelta");
                document.body.style.backgroundImage = "url('../Images/way_of_kings_bg.jpg')";
                break
            case "TramaPdL":
                nodoTramaVdR.setAttribute = ("class", "TramaNonScelta");
                nodoTramaPdL.setAttribute = ("class", "TramaScelta");
                nodoTramaG.setAttribute = ("class", "TramaNonScelta");
                document.body.style.backgroundImage = "url('../Images/words_of_radiance_bg.jpg')";
                break
            case "TramaG":
                nodoTramaVdR.setAttribute = ("class", "TramaNonScelta");
                nodoTramaPdL.setAttribute = ("class", "TramaNonScelta");
                nodoTramaG.setAttribute = ("class", "TramaScelta");
                document.body.style.backgroundImage = "url('../Images/oathbringer_bg.jpg')";
                break
        }
    }
    catch(e){
        alert("mostraTrama " + e);
    }
}

function gestoreLoadRomanzi(){
    try {
        nodoTramaViaDeiRe = document.getElementById("TramaViaDeiRe");
        nodoTramaParoleDiLuce = document.getElementById("TramaParoleDiLuce");
        nodoTramaGiuramento = document.getElementById("TramaGiuramento");
        nodoTramaVdR = document.getElementById("TramaVdR");
        nodoTramaPdL = document.getElementById("TramaPdL");
        nodoTramaG = document.getElementById("TramaG");
        nodoTramaViaDeiRe.onclick = mostraTrama;
        nodoTramaParoleDiLuce.onclick = mostraTrama;
        nodoTramaGiuramento.onclick = mostraTrama;
    } catch ( e ) {
        alert("gestoreLoadRomanzi " + e);
    }
}

All three start off with class = "TramaNonScelta", which has display: none, and when clicked they should change to class = "TramaScelta", which has display: inline. The IDs all match to the ones they have in the HTML document.

My alternate functioning way is to have a separate function for each book instead of a single one for all of them.

EDIT: I also have a very similar code for another program that instead of using .setAttribute uses .innerHTML and works without any problems (but my professor doesn't want us to use .innerHTML in this project)