You just add the below code in script editor or the js file in an app
//--------------------------------------------
<script type="text/javascript">
function Test() {
currentcontext = new SP.ClientContext.get_current();
var Sitecol_url = window.location.protocol + '//' + window.location.host;
var PageURL = Sitecol_url + currentcontext.get_url();
}
</script>
//------------------------------
