JS - Display div every 5 seconds with fade effect and close button

I have now looked for a solution on many other forums, but I can't find the right one, maybe someone here can help me

I have coded an notification popup on the left bottom of my site like:

I want now display my div class (notification popup) every 5 seconds with fadeIn() and fadeOut() effect and show it for 5 seconds, then the same again without stopping.

My Js Code:

var div = document.getElementById("show-div");

var myIntv = setInterval(function() {
    div.style.display = 'block';
}, 5 * 1000);

But it display my div just after 5 seconds and dont repeat it. Any one an Idea how can i do this?

My Second Question

I have also an little close span class in my popup window.

How can I stop the notification popup from appearing every second (If the first code works) and make the div class display:none; for the users current Session, if he clicked the close button?

I have tried it with:

$('#close-div').click(function() {
    clearInterval(myIntv);
});

But dont work.

Works with JS or must i use PHP Session?

First Question :
var div = document.getElementById("show-div");

var showFlag = true;
var myIntv = setInterval(function() {
    if(showFlag){
        div.style.display = 'block'; 
        showFlag = false;
    }
    else{
        div.style.display = 'none';
        showFlag = true;   
   }
    
}, 5 * 1000);

Second Question: Clear Interval should work.

$('#close-div').click(function() {
    clearInterval(myIntv);
});

Try this:

var div = document.getElementById("show-div");

var isShown = false; 
var myIntv = setInterval(function() {
    if(isShown){
        div.style.display = 'none';
    }
    else{
        div.style.display = 'block';
    }
    isShown = !isShown;
 }, 5 * 1000);