Session only cookies with Javascript

Yes, that is correct.

Not putting an expires part in will create a session cookie, whether it is created in JavaScript or on the server.

See https://stackoverflow.com/a/532660/1901857

A simpler solution would be to use sessionStorage, in this case:

var myVariable = "Hello World";

sessionStorage['myvariable'] = myVariable;

var readValue = sessionStorage['myvariable'];
console.log(readValue);

However, keep in mind that sessionStorage saves everything as a string, so when working with arrays / objects, you can use JSON to store them:

var myVariable = {a:[1,2,3,4], b:"some text"};

sessionStorage['myvariable'] = JSON.stringify(myVariable);
var readValue = JSON.parse(sessionStorage['myvariable']);

A page session lasts for as long as the browser is open and survives over page reloads and restores. Opening a page in a new tab or window will cause a new session to be initiated.

So, when you close the page / tab, the data is lost.

For creating session only cookie with java script, you can use the following. This works for me.

document.cookie = "cookiename=value; expires=0; path=/";

then get cookie value as following

 //get cookie 
var cookiename = getCookie("cookiename");
if (cookiename == "value") {
    //write your script
}

//function getCookie        
function getCookie(cname) {
    var name = cname + "=";
    var ca = document.cookie.split(';');
    for (var i = 0; i < ca.length; i++) {
        var c = ca[i];
        while (c.charAt(0) == ' ') c = c.substring(1);
        if (c.indexOf(name) != -1) return c.substring(name.length, c.length);
    }
    return "";
}

Okay to support IE we can leave "expires" completely and can use this

document.cookie = "mtracker=somevalue; path=/";