open a link to "localhost:4000"

I started a simple node.js server locally. It gives out an index.html. I want a link on the index.html to localhost:4000 to open the same page in a new window. But the Browser cannot read the protocoll in the new window, only if I hit refresh. How can I make a link with the adress "localhost:4000" ?

SERVER:

//make url 
  socket.emit('url', 'click here');

index.html:

socket.on('url', function (data) {
   $('#conversation').append('<a target="_blank" href="localhost:4000/">'+data +'</a>');
});