How to add target="_blank" to JavaScript window.location?

window.location sets the URL of your current window. To open a new window, you need to use window.open. This should work:

function ToKey(){
    var key = document.tokey.key.value.toLowerCase();
    if (key == "smk") {
        window.open('http://www.smkproduction.eu5.org', '_blank');
    } else {
        alert("Kodi nuk është valid!");
    }
}

Just use in your if (key=="smk")

if (key=="smk") { window.open('http://www.smkproduction.eu5.org','_blank'); }

I have created a function that allows me to obtain this feature:

function redirect_blank(url) {
  var a = document.createElement('a');
  a.target="_blank";
  a.href=url;
  a.click();
}

if you want to open a link in new tab window.open has a problem, my firefox detect a popup link by using window.open' and this is not good

I was handle this by using the latest comment

var anchor = document.createElement('a');
anchor.href = 'https://example.com';
anchor.target="_blank";
anchor.click();