var getAbsoluteUrl = (function() {
var a;
return function(url) {
if(!a) a = document.createElement('a');
a.href = url;
return a.href;
};
})();
// Test
console.log(getAbsoluteUrl("/some-relative-url"));
<html>
<body>
Check the console to see the output of getAbsoluteUrl("/some-relative-url")
</body>
</html>
body {
font-family: arial;
}