How to set a key to change style of a node?

Question

I'm doing an userscript of Greasemonkey and I want set a key to change style display:"" of none to block and vice versa of a node by press a key ("Home" in this case).

var bluebar = document.getElementById('pagelet_bluebar');
bluebar.style.display = "none";
document.addEventListener("keydown", function (e) {
    if (e.keyCode == 36) {
        showhideui();
    }
}, false);
function showhideui() {
    if (bluebar.style.display = "none") {
        bluebar.style.display = "block";
    } else if (bluebar.style.display = "block") {
        bluebar.style.display = "none";
    }
}

The solution was add == instead = in the conditions:

if (bluebar.style.display == "none")
else if (bluebar.style.display == "block")

Answer 1

Use == or === instead of single = sign in your comparison.
Check this link about comparison operators

 var bluebar = document.getElementById('pagelet_bluebar');
   document.addEventListener("keydown", function (e) {
       if (e.keyCode === 36) { //press "Home" key change to block/none
           showhideui();
       }
   }, false);
   function showhideui() {
       if (bluebar.style.display == "none") { //if is none
           bluebar.style.display = "block" ; //change to block
       } else if (bluebar.style.display == "block" || bluebar.style.display == "") { //if is block
           bluebar.style.display = "none"; //change to none
       }
   }

Ps: If there is only those two possibilities, you could even use a more synthetic way :

(bluebar.style.display == "block" || bluebar.style.display == "") ? bluebar.style.display = "none" : bluebar.style.display = "block";