Untitled

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width">
  <title>JS Bin</title>
</head>
<body>

<script id="jsbin-javascript">
function addUsername(list) {
  return list.map(function(x) {
   var d = new Date().getFullYear();
   x.username = x.firstName.toLowerCase() + x.lastName[0].toLowerCase() + (d - x.age);
    return x;
  });
}
</script>


<script id="jsbin-source-javascript" type="text/javascript">function addUsername(list) {
  return list.map(function(x) {
   var d = new Date().getFullYear();
   x.username = x.firstName.toLowerCase() + x.lastName[0].toLowerCase() + (d - x.age);
    return x;
  });
}
</script></body>
</html>